High excitement with my W-M indirect hot water heater.

Jean-David Beyer

Last night, around midnight, I heard a sort-of whistling sound in my house. Sounded like plumbing. I checked my high efficiency toilet: not that. I tried my darkroom with fancy valves, vacuum breakers, etc. Not there. I eventually went to the garage where the boiler and indirect water heater are, and the floor was about 1 inch deep in water from the open P/T valve on the indirect. Valve is about 6 years old and tripped the release, but the valve was still dumping water as fast as it could. I figured the valve failed, disconnect the thermostat to end the demand for heat, and turned off the supply water. I called the techie this morning, figuring to replace the valve.

Well it turns out the valve is just fine, that the thermostat in the indirect is faulty and demands heat under all conditions. So he is out getting a replacement.

Those valves are essential. If it had not released on over-temperature, I might not be typing this. Of course I know this, and everyone here knows it too. But I just had a demonstration of it last night.

JohnNY

I'm finding expansion tanks are necessary on all indirects in water metered properties. I'm sure it's pressure, not temperature, that tripped that relief valve. I see it all too often.
On my consulting jobs, I'm recommending them as part of any new IWH installation.

Jean-David Beyer

Hatterasguy: Perhaps you are right, this time. But what if my heating boiler failed at the same time, and the supply there, where there is no temperature relief valve is present (there is a pressure release valve there) at the same time. I would be in real trouble.

The boiler is set to supply 190F to the indirect, but there is 5F slop above and below, so the supply can be as high as 195F if it is working correctly.

But the valve did release, and not just a drip. So it either thought it was over 210F (where the valve is set (with what tolerance?) -- not adjustable -- or the pressure was over 150 psi --also not adjustable. And turning off the supply and turning on a hot water tap inside the house did not close that valve. But waiting 10 hours did close it. The techie and I both decided the valve opened on temperature. He then pulled the thermostat out and metered it at all settings of the thermostat and it demanded heat at all settings.

And Murphy's laws has not been repealed. Here are two of them:

1.) If something can go wrong, it will.
2.) If several things can go wrong, they will all go wrong, all at once.

It is just as well it did this, because otherwise I would not have known the old thermostat (now replaced) was defective and always demanding heat. The Caleffi mixer valve between the indirect and the house regulates the water supplied to the house to 122F so it comes out of the nearest load (my shower) at 120F. Where I mix it with cold to get my shower temperature.

Jean-David Beyer

JohnNY: My water is metered at the street, and I do not know if there is a check valve back there or not. I certainly have no check valve in my house, nor is there an anti-backflow valve in there either. (There is an anti-backflow valve in the makeup water line to the boiler.) I do not know if the code requires one now, but it sure did not require one in 1950 when the house was built. It did not even require a pressure relief valve on my boiler.

It seems to me that if the P/T valve opened on pressure, it would close again (calcium deposits permitting) when the pressure was reduced. I turned on the hot water in the house and it came out at normal temperature (reduced to 120F in the house by a Caleffi mixing valve at the indirect). So that should have reduced the pressure and the valve should close, at least to a dribble. And it did not. But allowing the tank to cool off for 10 hours did allow it to close.

It is now running normally with the new thermostat in the indirect. If this happens again in the next few months, it will indicate to me that it was both the valve and the indirect's thermostat. But for now, all is running OK.

Eternal maintenance is the price of comfort, I suppose.

jonny88

Tongue in cheek thats a funny comment Hatt.For what reason do you think a manufacturer will actually give a s**t.I am going through it with Budures right now.A few companies will void warranty of indirect if expansion tank is not installed regardless of whether it is required by code or not.You know how the blame game goes.

Tim Potter

I would definitely want to know why the HWT blew the safety valve.

If it relieved on pressure, thats one thing, an expansion tank & pressure regulator would solve that, not really the big safety issue, ( no myth busters water heater rocket danger) but why didnt the valve reseat? could be calcium deposits is suppose, better to stick open than stick shut for sure....

But If it relieved on TEMP thats a whole nother (& more important in my mind) thing.

not really sure the math works out, can an 80K boiler (if I recall correctly) put 1" water of 200* water in the gar floor & the outflowing water still be hot enough to keep the safety valve open? again if the valve relieved on temp, why didnt it close as the tank temp went down.

For what it worth, I put a temp gauge before my mixing valve to make sure my tank was at 140* before mixing down to 120*. Overkill, I know.

Glad you are safe,

Tim

hot_rod

I think once they pop on temperature the probe design prevents it from shutting off again. Is this true?

After a pressure release they usually shut down, or off again.

Jean-David Beyer

Since the valve is about 6 years old, I doubt it is still in warranty. It is a Watts 100XL-4 M7 and looks to be well made. Since it is still in there, it would be a pain to remove and return.

Once the thing cooled down, the valve reseated and did not leak, drip, weep. So probably not calcium deposits.

I wonder what the temperature tolerance on those valves is.

The one inch water on the garage floor caused no damage. It was all gone 12 hours later other than obvious color change in the concrete that disappeared by the end of the day.

I tried to buy a new P/T valve today to keep as a spare, because the next time it happens will be on Christmas eve, or New Year's eve when parts dealers are closed. My local Watts distributer was out of stock, and could not even find it in their computer system. It is still listed on Watts web site.

http://media.wattswater.com/ES-10L-100XL.pdf

In the meantime, I will want the overflow pipe modified so I can get it out without a tube cutter (even though I have one). Running a brass nipple from the valve past the edge of the heater, a brass or bronze 90 degree elbow, and then the copper downtube with an NPT thread on the top will fix it so I could replace the valve any time I wish.

So the things we know:

1.) The thermostat in the water heater failed always calling for heat, no matter what the position of the knob was, even after the thermostat was removed from the heater and allowed to cool down.

2.) The valve did open dumping hot water on the floor. At that time I pulled the test lever to open it more (who knows if it did; it may have been full open already) and allowed it to snap shut, The lever pretended it did that but it sure did not shut. I sure wish I had measured the water temperature coming out of the indirect at that point (there is a thermometer for that just before the mixing valve), but I would have had to turn the hot water on in the house to do that, and did not want to wait for that.

3.) The boiler did notice the demand from the indirect and was firing full on (94%). 80K BTU/hour is the maximum boiler input. And the controls are set so on hot water demand, it goes only to 94% 74,200 BTU/hour. Assuming the boiler runs at 100% efficiency (which, of course is does not).

4.) Next morning, I turned the cold water supply on to the indirect, and it went on, but the P/T valve had closed over night, confirming that it released because of over temperature.

5.) Opening the P.T valve with the test lever allowed water to come out, and allowing it to snap shut stopped the water from coming out. Probably insignificant deposits or dirt.

I think it would be quite a pain to test the temperature setting of the valve. I could put it in a pot of water and gradually raise the temperature. I do have a cooking thermometer that goes that high (actually much higher) and measures +|- 2F But I would need some way to detect if the valve opened or not without burning myself.

Jean-David Beyer

Well, I guess I identified the manufacturer and model number of that valve. I have seen cheap crappy Italian valves in the 1970s. I have seen very good (Caleffi) Italian valves in the last few year.
I have seen some really bad Chinese fittings, valves, etc. (But never any good ones.) The Watts looks pretty good, visually, but I have no idea if they have a good reputation in the field.

I would not feel good about saying not to buy Watts P/T valves based on one single data point. Perhaps I would feel differently had it failed shut and the whole thing exploded, or split a pipe in my concrete slab.

Bob Bona_4

What size tank? Wouldn't be the first time I've seen a 100xl discharge haphazardly from stacking or the spring getting "soft"

hot_rod

What is the boiler control set for, it certainly could be above 180, many go to 210F. Also just because the number indicates 180, doesn't mean it controls to that exactly. Good chance the tank exceeded the temperature that the valve could handle. Whatever that might be. keep an eye on the boiler, measure the output with an accurate temperature gauge.

My experience is the T&P valves fail, most often, the opposite way, they stick shut after years on non use.

Mark Eatherton

OK, so JDB has a problem with a relief valve, and Hatteras chimes in blaming a defective product and trashes a perfectly good company that has been in business for hundreds of years.

Hatt, you don't understand all you think you know about hydronics. There is a condition called thermal stacking that will cause the water temperature in the top of the tank to stratify and actually RAISE the water temperature above the maximum seen at the generator (boiler in this case).

You may have a good understanding of hydraulics, but you don't know all the parameters nor what really happens in the field.

The relief valve did exactly what it what designed to do. As water approaches the boiling point, the thermal portion of the valve is designed to begin slowly releasing water in an effort to keep things from going ballistic.

Another condition which can and has occurred on occasion, is a major drop in incoming water pressure which will cause the "180 degree F" tank to flash to STEAM, even though it is not at 212 degrees F. and the tank goes ballistic...

Rallying the troops to sue a manufacturer over a product that did exactly as it was designed to do is the reason this country is so screwed up now. No wonder we have trouble getting European companies to come to the US to provide their products. Too many lawyers and people who don't know what they are talking about telling people to sue the manufacturers for something they have no control over. Think before you speak, and think of what the consequences are for what you are saying, and if you don't know what you're talking about, remain silent and learn.

JD, your relief valve sounds like it is perfectly good and did exactly as it was designed to do. Unfortunate circumstance for sure, but the alternative, as you pointed out could have been much worse.... If memory serves me correctly, they recommend replacing the valve once every 5 years. Your insurance company COULD use that as a crutch to wave off any water damage claims. Improper maintenance...

ME

hot_rod

good points Mark. But how does the temperature in the tank go above what the boiler was outputting? I understand stacking and thermocline, but not the elevated temperature??

Mark Eatherton

Bob, I can't explain the exact physics, but I have recorded in numerous scenarios the stacking condition and have seen residual top water temperature increase by as much as 10 degrees F. over the maximum tank settings and temperatures seen at source shut down. A BTU is a BTU is a BTU, and when a bunch of them accumulate in the upper regimes of a static tank, strange things can happen.

In this scenario, essentially the tank and boiler were running free, bouncing off the boilers high limit and it sounds as though the limiting parameters of the boiler overrode themselves, compounding the issues of overheating and stacking.

Hatteras, I will pit my 39 years worth of field experience against yours any day. And I am NOT defending the manufacturer per se. Just pointing out facts.

If we trash talked every manufacturer whose product ever had issues, and they ALL have issues, and chase them out of town, what good is that going to do? I think a reasonable person would look at ALL of the facts presented, and go from there.

As far as water damage is concerned, the relief valve did exactly as it was designed to do. There are industry standards that have tolerances and ranges of acceptable operation. It sounds to me as though this relief valve was working as its supposed to. A "threshold" is the point at which the device should be a full relief capacity. I do not believe that it was not defective based on JD comments and the fact that after it cooled down that it shut itself off and isn't leaking. The fact that he has a physical plant in a location that doesn't have a floor drain serving it is an unfortunate situation, but that is not the relief valve manufacturers fault, is it?

I am done discussing this with you, because based on previous monitored conversations, you are never wrong, and you know more than anyone else on the face of the earth, and have all the experience you need to continue moving forward, and you have all of the answers.

Good luck in your journey.

ME

Jean-David Beyer

Tank is a nominal 40 gallon W-M tank-within-a-tank model, probably made by Triangle Tube in Belgium. The inner tank that holds the domestic water, is 36 gallons, and the outer water jacket that holds the boiler water is 6 gallons. One of these (Ultra Plus 40):

http://www.weil-mclain.com/en/multimedia-library/pdf/weil-mclain-pdf/products/water-heaters/indirect-fired-water-heater/indirec_fired_water_heater_plus_indirect_fired_water_heater_manual.pdf

I could see how stacking could make the water at the top hotter than some at the bottom. Hotter even higher than the temperature set on the thermostat. But I do not see how it could get higher that the supply temperature from the boiler. As far as getting 195F water to flash, the pressure would need to be reduced to 10.3 psi absolute, whereas it is usually closer to 55 psi absolute. Even if I had all the output and drain valves on that indirect open, the pressure would not go below 14.7 psi absolute.

The thermostat is in a well suspended from the top that reaches a couple of feet down. The bulb is at the bottom end of the capillary tube, but the tube probably measures temperature too, though not as much. The dial, however, is not calibrated. I calibrate the heater so that when there is a fairly large hot water demand, the indirect calls for heat and shuts off between 155F and 160F. That way as the tank cools, it does not call for heat until it gets town to 140F. I measure the temperature at the hot water entry to the Caleffi mixing valve that is set to deliver 120F to the house. It sometimes goes up to 121F. Those thermometers are about 2 1/2 inches in diameter and have a mark every 5F. I can easily read them to 1F, but I do not know how accurate they are.

The boiler has a digital thermometer that is precise to 1F, though I do not know its accuracy. It is set to supply 190F water to the indirect, so it should be in the range of 185F to 195F supply, and the return temperature is also measured, but I have not looked at that lately. It is usually around 20F lower than the supply when the call for heat is satisfied.

But I do not see how the water in the indirect can exceed the supply temperature from the boiler to the indirect. The boiler does not like it if the return temperature is higher than the supply temperature. If the return is greater than the supply by >58F, it will shut off for 30 seconds and reset. If that happens 20 times, it will lock out and need to be manually reset.

If the return is >10F more than the supply for 10 minutes or more, it will shut off. It will reset once the situation clears.

If boiler output exceeds 200F, it locks out and must be manually reset.

RobG

I personally have never had any warranty issues with Watts. If I had a problem with a product either the wholesaler or the rep took care of it. I would not expect to get any support on a six year old T&P valve that was just doing it's job.

Jean-David Beyer

"In the case of the OP, the Watts valve most definitely released on temperature way below its 210°F setpoint causing a lot of damage to his home. Just who do you think is responsible for that?"

Not quite accurate. The boiler and indirect are on the concrete slab in my garage. While water did get up to about 1 inch deep around the indirect, it dissipated after I turned off the cold water supply (and I turned off the demand to the boiler before I did that). So the concrete slab of my garage got wet. By morning all visible water was gone and the slab looked as though it had gotten wet. By noon, all traces of the adventure were gone except for the bill I will be getting for a new thermostat assembly for the indirect, and an hour's labor from my heating contractor.

hot_rod

Mark Eatherton said:

Bob, I can't explain the exact physics, but I have recorded in numerous scenarios the stacking condition and have seen residual top water temperature increase by as much as 10 degrees F. over the maximum tank settings and temperatures seen at source shut down. A BTU is a BTU is a BTU, and when a bunch of them accumulate in the upper regimes of a static tank, strange things can happen.

Actually the tank manufacturers are trying there best to increase the stacking. The Lochinvar stratification tanks claims a 30° stacking in their tank. Some of the Euro designs are pushing 40° delta from top to bottom. tall skinny helps

Idronics 17 is all about tanks, stratification, thermoclines, etc. stay tuned.

I'm from the Show me State, I need to see and experience that temperature overshoot. If the supply from the boiler to the tank absolutely never exceeds 180°, I don't see a tank getting to 210°F at the relief, or even to 180, as there is no 100% transfer.

No IF the boiler over ran stepping and went to 210F high limit, that's another story. hard knowing, not being there to witness it.

Bring the infrared camera by, lets have a look at a naked tank in the lab.

RobG

@ to replace the T&P, but since it is six years old and I recall you saying that it gets tested every year, the spring inside is probably weakened a bit, I would recommend replacing it.

Jean-David Beyer

"In this scenario, essentially the tank and boiler were running free, bouncing off the boilers high limit and it sounds as though the limiting parameters of the boiler overrode themselves, compounding the issues of overheating and stacking."

I imagine the boiler cycled between 185F and 195F. It is a mod-con, and it may not have even hit the high limit. As the supply to the indirect approaches the set point, the firing rate goes down. As it passes the set point the firing rate goes down even more. I normally do not see it hit either of these set points because the modulation can deal with it.

I assume the thermostat in the indirect failed, because it was still failed the next morning and asking for heat even when we turned the setting all the way down. And the tank was pretty hot. Normally, turning that thermostat down will stop the heat demand. So that is failure #1.

Now the next question is, did the P/T valve fail and open when it should not have? Or did something else fail and the temperature in the indirect really go over 210F? If the boiler was running correctly, the maximum out put temperature would have been 195F. If that failed, other safeguards would have shut down and locked out the boiler once the output temperature hit 200F, and that did not happen.

What are the design parameters of those P/T valves? Its name plate says 210F. Could it really be 10F to 15F lower than that?

They always say I did not change anything and this happened. I do not say this. Five months ago, I put that Caleffi mixing valve in and raised the temperature of the tank from about 120F (not measurable) to between 140F and 160F. And the thermometer giving those readings is identical to the one giving the 120F to 121F at the output of the mixer valve. And I can put my hands in the hot water (briefly) coming out of a tap in the house. It measures 115F there with a thermometer that reads about 2F low.

hot_rod

If you set the indirect control at 160°F , for example, and it is near the bottom of the tank. And IF the boiler runs to 195°F on indirect call, then you could possibly stack I'd guess around 190°F at the top of the tank under no flow, no recirc conditions.

Still doesn't explain the relief, if in fact it went off on temperature protection. I imagine some + or - accuracy in that relief valve, hard to hit 210°F on the money. Could the probe be coated or compromised? Does the probe extend into the tank, and in the very top 1/3?

Mark Eatherton

JD, I do have a lot of experience with that tank in a tank design, and it was not good. I dealt with the larger tanks (119 gallons) and the problem we kept experiencing was the inability of the boiler to satisfy the tank stat, causing nuisance "no heat" calls. The manufacturers rep recommended pulling the sensor higher in the tank. Bad solution, because it would affect the tanks stored volume and cause shortages during peak demand.

I think in theory it's sounds like a good idea, but in reality, there is no scrubbing action on the inside of the tank to wash the BTU's off of the heat transfer surface like you'd see in a FPHXer.

We saw significant thermal stacking in those heaters and also saw the T&P relief valves seeping from high temperature conditions. Boiler in these cases was set for 180 plus/minus a 5 degree differential, and there is always slop in mechanical control devices, so possibly warmer than that, but no where near 210F.

I think it is the lack of Reynolds numbers (extremely low fluid velocity because convection current is only potable fluid moving function) on the inside of the potable tank that causes and compounds this problem. Having a pump between the inlet and the outlet of the tank would give the scrubbing action, but would then cause mix and dilution which would then affect the hourly output capacity of the water heater.

The thermal actuator on these devices is parafin wax and powdered copper. The copper serves as a conductor, and the wax expands when heated and that is what causes the valves thermal relief capacity to kick in. It's not like a fusible link that is set to fail and allow a wide open condition at a given temperature. It is a proportional operation, and it has to begin before the water gets to the boiling point.

I attempted to find the specifications for ASME Rated, ANSI Z21.22, the standard by which these valves are built, to no avail. By the way, Watts recommends testing annually, and inspection and replacement as needed every three years.

As for replacement, you don't need to completely drain the tank(s) to replace the device. Simply relieve the pressure the boiler pressure to static, then relieve the potable water pressure to zero, then close all connected tappings on the potable side to hold the water in a neutral static condition.

Pre dope the replacement valve, double check that there is no residual pressure in the potable side of the tank, or the boiler side of the tank, then unscrew the relief valve out of its tapping and quickly install the new one. You might lose a little water, but no big deal. I've replaced drain valves on the bottoms of tanks using this method successfully, but you don't have to worry about that in your case, because there is no drain valve on the potable side of the tank. But you already knew that.

When re-pressuring the tank, you need to follow the manufacturers recommendations or you will collapse the inner tank. That design of tank actually "balloons" on the potable size with pressure fluctuations on the potable side and can cause pressure fluctuations on the boiler side.

HR, I'd be glad to bring my IR camera down to Know It All Lane, but we won't be able to do the test because looking at a bare naked tank won't create these conditions. Too much loss and radiation occurring. The tanks in which I have seen it occur were well insulated, as were the pipes, and I recorded these conditions using thermistor data loggers.

One was a child abuse case for a local county. I'd share that information but due to client private information, no can do.

The other was on an apartment complex that was sued by a tenant for scalding conditions, also protected information. My instrumentation might have been off by a couple of degrees, but not THAT much.

I am also aware that the manufacturer had protested the ASME requirement for these tanks in Colorado because it is virtually impossible for the tank to transfer 200,000 btuH @ high temperatures due to the lack of differential in temperature between the two tanks. They were successful in getting the Colorado State Boiler inspectors to back off of their ASME rating requirements.

If the tank is completely cold, and under extreme loads, with a hot boiler it will transfer more than 200K btuH (one of numerous ASME required thresholds) but will not reach an unsafe condition because the temperature relief function would kick in before the tanks could become ballistic at higher tank and boiler temperatures.

To be safe, I think I'd go ahead and replace the T&P relief valve on your tank so you can sleep at night.

ME

Jean-David Beyer

@ to replace the T&P, but since it is six years old and I recall you saying that it gets tested every year, the spring inside is probably weakened a bit, I would recommend replacing it. "

Interesting how people let things escape them. I have the same problem, so I am not upset by this. BUT

I did not say I tested the T&P every year. I said that the indirect manufacturer said to test it every year, and if I remember correctly, Watts say the same thing. However, my heating contractors (both the installing contractor and my current contractor) said never to test these valves. And, unfortunately, he put the drain tube in according to code, within 6" of the floor, so I cannot get a bucket under it for test purposes.

In my opinion, this is probably an old wife's tale. True if the valve has not been tested in years, but probably not true with a new valve tested regularly. In any case, I would always want a replacement valve on hand in case testing it resulted in its not closing properly. I have a spare pressure relief valve for the heating boiler, but do not yet have one for the indirect.

When I bought the house, the P/T drain tube ended about a foot above the floor, so the bucket fit there just fine. And it sometimes needed a bucket because if I released it once a year, it would seldom close completely on the very first try, but it would after two or three tries.

My plan, as I said before, is to replace the current draining tube (all copper tubing and an elbow) with a brass horizontal nipple long enough to reach past the edge of the indirect, a threaded 90 degree elbow, and a vertical tube with a threaded end at the top. And I will have another such tube, about a foot shorter than code, that I will put in when testing, so I can test the thing and, the case arising, replace the valve when needed. I suppose I could do that all myself if the dope on the existing threads has not seized up. The installer used both dope and teflon tape, so perhaps it will come out.

Jean-David Beyer

"The valve , which has a setpoint of 210°F, released at 190°F."
Not quite what I said. I know the valve has a nominal setpoint of 210F. It says so on the little plate around the test lever. But I do not know at what temperature it released.
Perhaps 190F or 195F is correct, but I regret that I did not measure it. I really wanted to turn the water off.

My boiler is programmed to supply water in the range of 185F to 195F to the indirect. It starts up lower, of course, since my heating zones have much lower upper limits. And there are various forms of instrumentation on this boiler. There are thermistor sensors at the input and output of the heat exchanger. There are thermistors near the return part of the closely spaced Ts, and near the supply part of them. I also have a dial (2 1/2 inch) thermometer at the output of the indirect just before it enters the HOT input of the Caleffi temperature balancing valve. I also have one at the output of the caleffi valve where the mixed water goes to the house. I also have a one-inch dial Weston dial thermometer that I can use to measure the temperature of hot water coming out of the valve nearest the hot water heater but in my wash basin of my house. This last one reads low by 1 1/2 to 2 degrees F.

For the Indirect, the thermistors at the entry and exit from the boiler's heat exchanger are used. I can read them to within 1 degree F. Notice, this is the precision, not the accuracy. But it they do agree with the tridicator in the boiler that was new with the boiler installed in May 2009 and seems to still be working correctly. That is the only practical way to measure those temperatures unless I install thermometer wells in the supply and return to the indirect, and there is not really any room for those except near the indirect. But I do not have a coupla hundred bux to pay to have that done.

Now the indirect does not really have any indication as to what its thermostat is set to. It has a knob with a pointer, and a scale with arbitrary markings on it. What I now do is set the thermostat to any old thing, hoping it is less than shut off at 140F and start it up. Once it is satisfied, I run hot water pretty hard from my wash basin and observe what the indirect output temperature is. I want it 140F minimum, and take what I get on the hot side. That is usually 155F to 160F. Under these conditions, the Caleffi mixer valve puts out water between 120F and 121F. Its tolerance is a little greater than that, but I must be lucky.

By the way, I do not have a recirculation setup on my hot water lines. I wish I did. So the indirect can do stacking. And it is possible that the water at the top gets to be hotter than the water at the bottom of the tank, but I set its thermostat by measuring the water temperature of the water coming off the top through the same tapping as the relief valve is located.

So it seems to me that if the valve is good, then the boiler has had to be delivering water to the indirect in excess of 210F, and I do not like to think that, because in addition to the operating controls that should keep the output temperature under 195F, there is a safety control that locks out the boiler if the output temperature hits 200F. To get things up to 210F, the operating control and the safety would both have to fail (in addition to the thermostat in the indirect that did fail).

Jean-David Beyer

"The valve is designed as Mark stated to slowly open when the temperature approaches the boiler point. Since it does not operate like a switch, there must be a range over which it operates. Its stated temperature is 210°F but we know that it is impossible for the valve to START to open at that temperature because it could most certainly not be fully open at 212°F.

So, it must start to open at something less than 210°F."

I do not know about temperature relief valves, or even pressure relief valves as used on domestic boilers.

I do know about pressure relief valves (safety valves) as used on steam railroad locomotives, and they open very fast on over pressure. And they stay open until the pressure drops considerably, when they shut off very quickly. The British even call these things "POP" valves. POP is not an acronym for anything.

You may well be right about this, but think about this.

The boiler manufacturer has the default water temperature for the indirect set at 190F, and the slop set at +|- 5F, so it certainly should be producing the supply to the indirect in this range if operating correctly. And the emergency lockout is at 200F.

Now the indirect comes with the Watts P/T valve, and I do not think I would want the temperature relief set any higher than 210F, as it is now.

The Indirect has a dial where the recommended starting temperature is indicate by a white triangle. If set to that point, the indirect runs hotter than 140F as measured by the water coming out of the indirect. It is definitely too hot for use in the house, so when I first got that boiler and indirect, I set that thermostat considerably lower and got about 120F in the house at the times I measured it. Later experiments showed that the thermostat had a slop of about +|- 10F

Since I wanted to run the indirect no lower than 140F for anti-Legionella reasons, I had a Caleffi mixing valve installed and set to deliver hot water at 120F to the house. And Caleffi recommend hiving the hot water supply at about 20F hotter than the delivered temperature, which means at 140F for me. And with +|- 10 Slop in the indirect, I pretty much need nominal 190F supply from the boiler, because, when it is lower (say 175F), the recovery time is too long.

I imagine what happens normally is that the thing all runs and the supply temperature is 185F to 195F, but the domestic water in the tank is in the range of 140F to 160F (because the thermostat stops calling for heat when the tank gets that hot). But when the thermostat failed, the water temperature went up to 195F and stayed there. The valve opened. Maybe just a trickle at first, but the boiler was running flat out at 80,000 BTU/hour (input) and then the valve opened more. It seemed to be full open when I got there. It did manage to flood the floor. It was not a trickle. Supply from the water company is 3/4 inch copper tubing all the way to the indirect, and the drain pipe from the relief valve is also 3/4 inch. It may not have been coming out at 40 psi, but it sure was not a trickle. Perhaps the cold water coming in with the relief valve full open cooled the water down (on the theory that 80,000 BTU/hour is not enough to keep the temperature up with the relief valve full open).

And maybe the relief valve is designed like railroad steam engine pressure relief valves, and will not close until the temperature has dropped a lot. As mine did when I turned off the boiler supply and then the cold water supply.

Bob Bona_4

What's your take on the tank in tank indirects, Hat? Triangle Tube?

Bob Bona_4

Gotcha. My only issue with FPHXers is water quality or lack thereof fouling them.

Bob Bona_4

And really, the onus should be on the owner to maintain acceptable water quality, not really to find the "most tolerant" equipment whether it's the tank in tank (more tolerant) or a FPHX (least). Such is life.

rick in Alaska

And if you test the valves on a regular basis, as you definitely should, they are not prone to sticking either open or closed.
Rick

4Johnpipe

One thing that I did not see mentioned...why was the the relief valve valve still open while it was filling with cold water? As far as manufacturers I'm not in love with that boiler. Could it be possible the boiler was running hotter than the setting? If the TP valve was full open open it was filling with cold water...this should have kept the tank temp down...the placement of the TP valve going through the tank in tank design would be reading hotter than normal boiler water....just a thought...

Jean-David Beyer

"The setpoint on the boiler, at 195° is above the point where the temperature relief will let go on the indirect."

The setpoint is 190F (+|- 5F) the default boiler setting. I am surprised you say that a 210F temperature relief valve starts to open at less than 195F. I cannot say you are wrong, but I have trouble believing it. I cannot find published listings for the tolerance and operating ranges of these valves. Where do you get your data?

"So, the same exact scenario will occur again if the circulator to the indirect runs constantly."

Quite possibly, but I have been running it like this since early January, and that P/T valve did not open until a few days ago. I suppose that is when the thermostat failed and let the indirect tank get up to possibly 195F, where it should have stopped demanding heat at 160F.

"The valve opens somewhere considerably less than 190-195°F and allows cold water to entire the tank."

As I said, this could be so, but I have trouble believing a valve rated at 210F would open so soon. Where did you get this data?

"It does take awhile for the sensor to cool back down and close. I'm uncertain as to whether it closes significantly below the start of opening. The mechanism in the valve doesn't appear to allow that."

I have not taken such a valve apart, so I do not know what is inside. Neither have I seen a diagram of its insides, so I just do not know. If it works something like a Klixon thermostat, it would open at some temperature and would need to cool down 5F or 10F to close again. But so what? If the hysteresis were too small, it would weep all the time near the set point, and that is usually not a good idea. It is a very bad idea for a pressure relief valve.

"Do you really need 190°F to get the indirect to perform satisfactorily for you? If you're storing at 135°F, that's a whopping 55°F differential."

I want to store the water at 140F minimum. The thermostat has about 20F hysteresis, so that means it will run from 140F to 160F. If it cannot get slightly above 160F, the heat demand will never stop. I initially had the boiler set to 175F (170F to 180F) and that was not enough to end the heat demand. So 30F difference to 190F and 50F to the nameplate release temperature on the P/T valve. That should be just fine. Even if it got up to 195F, it should be 15F to release, if the release action is quick. They sure do not want it to get to 212F at sea level.

"As an aside, I've been so thoroughly disgusted with the performance of the indirects due to minimal coil size (race to the bottom), that I am going to install one of these and dispense with the indirect tank completely"

The WM Ultra Plus indirect is a tank within a tank design where the domestic inner tank (stainless steel) is 36 gallons completely surrounded by the 6 gallon outer tank with the boiler water in it. The hot water supply from the boiler goes in the bottom and the warm water out comes out near the top. The area of the inner tank must be considerable. When it drops 20F over night, it reheats in about 10 minutes. Probably enough surface area.

Jean-David Beyer

"The nature of that design requires a range. It's not a switch. I do not know the point where it begins to open. However, if it were to start to open at 210°F, like it should based upon its label, it could not be fully open until it reached somewhere around 225°F due to the nature of the design. "

Sure it requires a range. The question is, what is that range and where is it? A temperature relief valve could be designed to have a range of 2F or 5F, or almost anything you care to specify. The tighter the range, the more complex and more expensive the device would be. I think the terms differential and hysteresis are pretty much the same in this context.

Imagine one takes such a valve and slowly increase the water temperature. At some point the valve opens, quickly or slowly as the water temperature increases until the valve is fully open. Call that temperature the high point. Now slowly reduce the water temperature until the valve closes again. That temperature is the low point. You can call that the differential. If the high point is not the same as the low point, then if you plot the curve, you will not get a line that retraces itself. You will get a sort of rectangle (ideally, though the shapes will, in practice, be sloppier), and the area of that is usually called the hysteresis.

Now steam pressure relief valves on railroad steam locomotives had hysteresis on purpose because it was not desired to have those valves open gradually, nor was it desired to have them close gradually becaust that would wear out the valve seat too quickly. At 150 psi and up (a few boilers were designed to run at about 300 psi, but 225 psi was more usual), that can happen quickly.

Jean-David Beyer

"The hysteresis of the thermostat itself cannot be 20°F unless it is defective. If you set the thermostat at something near 140°F and send something near 175°F to the tank, the thermostat will satisfy, eventually, unless it is defective.

So, I am quite sure you have a measuring error or a hardware error."

Sure it will satisfy, but instead of taking 10 to 15 minutes, it takes closer to 45 minutes and I did not want the boiler running that long to heat the hot water since in the wintertime, the time heating the indirect is time the house is not getting heat. That is why I raised the boiler temperature, when responding to a call from the indirect, to the boiler manufacturer's default recommended temperature.

I do not see how you infer a measuring error or hardware error.

Jean-David Beyer

"If it drops to 120°F overnight and you reheat it with 190°F SWT, of course it is going to perform like a champ."

Right: it does.

"Let it drop to 120°F and try to reheat it with 160° SWT and see how long it takes to climb to 140°F. If that time is "reasonable" then I'll be convinced. "

I guess it depends on what you think a reasonable time is. I thought it was too slow at 175F. If that indirect's thermostat had tighter limits, I would set the low point at 140F and let it shut off at 150F. But it doesn't.

"Nobody wants to run a boiler at 180°F to keep an indirect at 140°F. But, that is what most people must do because the performance of the indirects won't allow less and still manage a decent recovery time. "

Well, my boiler is a mod-con and runs at different temperatures depending on whether it is supplying the indirect (now 190F), baseboard heaters, or radiant slab. The latter two have outdoor reset and run at much lower temperatures.

hot_rod

Some tech info regarding a T&P valve we manufacture for the Euro market.

90°C (194F) listing, starts to open "leaks" between 89- 94C
complete opening at 3-4C additional temperature
So 89+4=93C or 94+4=98C

Closes off at 85C

90°C = 194°F

We have added a 95°C valve = 203°F

hot_rod

Maybe, Hat you should clear up the difference between differential and hysteresis, that may be some of the confusion.

As I understand it, an open on temperature rise control, like a DHW aquastat with a typical 10° diff would turn off (open) at 140°, back on (close) at 130°.

I understand hysteresis to be, the control operated around the 140 setting, so on at 135°, off at 145°.

Is that how you understand the terms?