PSI at boiler exceeds 30psi when hot in 4 story house

DIYorBust

psb75 said:

I'm not so sure that having a pressure gauge at the bottom of a DIRT SEPARATOR is the best place to get an accurate system pressure reading. Where is the "air" that you say collects in the upper radiators coming from? Your system should be closed to air. Once it is removed, it should not reoccur--regardless of system pressure.

It also reads the same at the purge valves. I'm not sure where the air is coming from, maybe microleaks? Maybe it's elsewhere in the system left over from the previous drain down? I don't know. But it's definitely not the case that if the system is full of water the pressure can be reduced to zero and expect it to stay full. If that were the case we would not need the prv/fill valve.

DIYorBust

psb75 said:

I don't see any fill-valve and back flow preventer. Where might that be ? And what might the fill pressure be set at? It usually comes "off the shelf" factory-set at around 12-14 psi. Do you perhaps have that fill pressure "boosted" too much?

It's on the left and it's set to 22, half inch that plug into the tee on the right side of the navien manifold primary loop.

hot_rod

It's the actual pressure, measured with an accurate gauge, at the relief valve location that you want to know. If the valve is at the top of the boiler, that helps some. Static pressure at that point would give you the elevation that the water level is at. And of course dynamic pressure at the valve will indicate when the valve will seep.

The unknown is the pressure tolerance of the relief valve, I've never seen that published by manufacturers. I'd suggest 5 psi below the rating of the valve would be a safe number to stay at or below.

Maybe you can "tank" your way out of this, perhaps two# 60 since we are all guessing at system capacity, no harm in oversizing expansion.

While you do that I would still move the PONPC to the Dirtcal loction.
What do you have to lose. Still less $$ than a HX isolation.

Daveinscranton

I would get a nice accurate gauge and plumb it in.  I would look in the manual.  Should say in there something about maximum safe boiler pressure.  You may be able to put a good 50 psi pressure relief valve on and be done with it.  Cheaply too.  My guess is that you could do it anyway but I would feel better if I saw it in print in the manufacturer’s literature.  

Best wishes 

JR3_Home_Performance

I didn’t read all the comments but it seems that the easiest solution is lowering max water temperature as someone else suggested. I have a radiator heated victorian in upstate NY. I don’t need my water temp to go over 120F (ODR on primary loop) on the coldest of days after I insulated the house. Also I use the viridian sensors and set it to delta T mode. Most of the time it runs on the lowest speed. Do you have to run it on max? My boiler is about a 100kbtu output and I don’t use a reset sensor connected to it itself. The boiler will modulate to target the upper temperature I set for it (140F I think?). With that the boiler is cranking out maximum btu sometimes and still the pump doesn’t seem to need to go full tilt to move the heat energy. Granted the system was originally a gravity system so pipe sizing is huge other than the 1” pex I used to connect about 20ft away. 

Daveinscranton

Last thought.  If it has to be a 30 psi pressure relief valve, maybe buy a few different PRV’s, from different manufacturers, and test them all for actual pressure.  You may find one that is 31 pounds vs 26 pounds etc.  You could install whichever 30 pound relief valve that tests the highest.  

JR3_Home_Performance

.

hot_rod

Which model Navian do you have? the ASME tag should show the pressure rating, here is what their manuals show??


If it is a tankless water heater, it too should be 80 psi. Or more.

EBEBRATT-Ed

My original post (4th from the top) mentioned checking the tag on the HX and contacting Navien to see if a higher pressure relief valve could be installed.

This should have been one of the first thing looked at

DIYorBust

psb75 said:

I'm not so sure that having a pressure gauge at the bottom of a DIRT SEPARATOR is the best place to get an accurate system pressure reading. Where is the "air" that you say collects in the upper radiators coming from? Your system should be closed to air. Once it is removed, it should not reoccur--regardless of system pressure.

Well I suspect the air is coming from air in the system that accumulates at the top, or maybe from small leaks? Threaded connections that leak water slower than it evaporates maybe? I don't know really, but it does come. I get the same readings on the purge valve as the dirtmag.

DIYorBust

psb75 said:

The unknown is the pressure tolerance of the relief valve, I've never seen that published by manufacturers. I'd suggest 5 psi below the rating of the valve would be a safe number to stay at or below.

Maybe you can "tank" your way out of this, perhaps two# 60 since we are all guessing at system capacity, no harm in oversizing expansion.

While you do that I would still move the PONPC to the Dirtcal loction.
What do you have to lose. Still less $$ than a HX isolation.

Well, I actually don't really care that much what the pressure is at the relief valve, but what the pressure is in the boiler, because as far as I can tell, that's the only component that cannot tolerate pressure over 30. The relief valve could be easily raised or replaced.

DIYorBust

Daveinscranton said:

I would get a nice accurate gauge and plumb it in.  I would look in the manual.  Should say in there something about maximum safe boiler pressure.  You may be able to put a good 50 psi pressure relief valve on and be done with it.  Cheaply too.  My guess is that you could do it anyway but I would feel better if I saw it in print in the manufacturer’s literature.  

Best wishes 

The boiler specs say 30 psi. That is really the chief concern that I have. In fact I think it's unlikely that 33 or 32 is going to cause any damage to the boiler, but I try to do things the right way and follow the manufacturers instructions because I'm not a boiler engineer. Actually the T&P valve is not currently opening with the pressure in the boiler reading 33 psi. So either the pressure is different at the valve than the boiler, or the boiler pressure sensor is wrong as I don't think the T&P valve is defective.

DIYorBust

Daveinscranton said:

I would get a nice accurate gauge and plumb it in.  I would look in the manual.  Should say in there something about maximum safe boiler pressure.  You may be able to put a good 50 psi pressure relief valve on and be done with it.  Cheaply too.  My guess is that you could do it anyway but I would feel better if I saw it in print in the manufacturer’s literature.  

Best wishes 

'

JR3_Home_Performance said:

I didn’t read all the comments but it seems that the easiest solution is lowering max water temperature as someone else suggested. I have a radiator heated victorian in upstate NY. I don’t need my water temp to go over 120F (ODR on primary loop) on the coldest of days after I insulated the house. Also I use the viridian sensors and set it to delta T mode. Most of the time it runs on the lowest speed. Do you have to run it on max? My boiler is about a 100kbtu output and I don’t use a reset sensor connected to it itself. The boiler will modulate to target the upper temperature I set for it (140F I think?). With that the boiler is cranking out maximum btu sometimes and still the pump doesn’t seem to need to go full tilt to move the heat energy. Granted the system was originally a gravity system so pipe sizing is huge other than the 1” pex I used to connect about 20ft away. 

Currently we are installing radiators and insulating, so perhaps I can lower the water temp in the future, although the top floor which has the roof exposure also has baseboard, so increasing the volume of radiation would also increase the height of the system a little. Nevertheless, lowering the temperature is not ideal with an indirect water heater zone. I keep the water in the tank close to 180 and mix it down. The loss of recovery time and storage capacity would make the hot water supply inadequate if I turned it down much unless I upsize the indirect. The risers are 1.25" in my system.

DIYorBust

Daveinscranton said:

Last thought.  If it has to be a 30 psi pressure relief valve, maybe buy a few different PRV’s, from different manufacturers, and test them all for actual pressure.  You may find one that is 31 pounds vs 26 pounds etc.  You could install whichever 30 pound relief valve that tests the highest.  

hot_rod said:

Which model Navian do you have? the ASME tag should show the pressure rating, here is what their manuals show??


If it is a tankless water heater, it too should be 80 psi. Or more.

It's an NHB-150 and the rating is 30PSI.

DIYorBust

EBEBRATT-Ed said:

My original post (4th from the top) mentioned checking the tag on the HX and contacting Navien to see if a higher pressure relief valve could be installed.

This should have been one of the first thing looked at

The boiler specs are 30psi, are you saying it's possible that the HX itself has a higher rating?

Drew_10

I have a couple of observations and questions:
1. Is it necessary for the pumps to be on hi speed?
2. Have you tried reducing the boiler pump speed? I’m thinking it’s a modulating gas valve and the gas will throttle back to maintain supply set point?
3. I see the Grundfos circulating pump appears to serve the lower level(s). The supply line drops down several feet. This is an obvious air trap and I question the ability of the pump to remove the air from this line. Your pump may be on hi speed and not moving the rated water. Your hose connected indicates makeup water has been added and the introduction of air is a net effect of it being driven out. Again, on the air trap I mentioned I would have a manual air vent.
4. Again, on the possible air trap mentioned, I see the same drop on what appears to be a return line (heat trap?) near the water heater just above your hose.
5. I don’t see the make-up valve anywhere and how it’s tied in.
6. With a cold system standing pressure of 22 psi, as a test only, has a technician tried turning off the makeup water and then bring the boiler up to temperature? What was the result? Under the same test, what effect does changing the boiler pump speed have on the pressure?
7. I don’t see any viable pressure gauges on the system.

Daveinscranton

My mod con boiler’s digital internal pressure gauge reads about 2 pounds higher (static pressure, with all pumps off) than my high quality 4” analogue pressure gauge plumbed in maybe 12” lower than the location of the mod con’s digital sensor.  I trust the 4” gauge.  The mod/con’s gauge reads to 1/10’s of a pound. Deceptive to look at, in my case.

Even in today’s cost cutting world, I find it hard to believe that anyone would engineer a boiler that would let go at just over 30 pounds.  The very fine print, on mine, a Triangle Tube, says that you can use a 50 pound pressure relief valve if the situation (tall structure to be heated) calls for it.  

Ed suggested a call to Navian.  Sage advice.  You will want to talk to the engineers.  And the engineers will not be the ones who man the phones.  

A solution will be found.  And it must, and will be a very safe and workable solution.  

best wishes 

hot_rod

Problem I see is different models of Navians have different pressure ranges. The one you have in fact shows 30 psi, others models that I posted above allow 80 psi?? Seems odd. The plate welded on the front the ASME tag is the final word on what that heat exchanger is officially rated for.

Personally I'd throw a 40 psi B&G 790 relief valve on it and call it a day.

Drew_10

I forgot to mention your expansion tanks.
1. I like to set my expansion tanks about 7 to 5 psi below my makeup water pressure setting with a cold boiler. I like to know my expansion tanks are doing work. So if I’m setting up a 22 psi feed pressure, I’m going to adjust my expansion tank pressure to say 17 psi.
2. Also the expansion tanks should be serviceable. I always install an isolation valve for each tank and locate a union or drain valve between the isolation valve and the expansion tank. Give yourself some room to work… they don’t need to be close to each other. It is important to drain the water off of the expansion before checking or setting the tank pressure. You can’t do this in your setup. A tank could have a small leak and you possibly wouldn’t know until water shoots out of the schrader valve. But this could effect the tanks operation. This recommendation and the one I made yesterday regarding the air traps is where I would be looking first.

hot_rod

Drew_10 said:

I forgot to mention your expansion tanks.
1. I like to set my expansion tanks about 7 to 5 psi below my makeup water pressure setting with a cold boiler. I like to know my expansion tanks are doing work. So if I’m setting up a 22 psi feed pressure, I’m going to adjust my expansion tank pressure to say 17 psi.
2. Also the expansion tanks should be serviceable. I always install an isolation valve for each tank and locate a union or drain valve between the isolation valve and the expansion tank. Give yourself some room to work… they don’t need to be close to each other. It is important to drain the water off of the expansion before checking or setting the tank pressure. You can’t do this in your setup. A tank could have a small leak and you possibly wouldn’t know until water shoots out of the schrader valve. But this could effect the tanks operation. This recommendation and the one I made yesterday regarding the air traps is where I would be looking first.

You will lower the acceptance volume a bit with this method, so if he is close already on expansion space, better not go too low on tank pre-charge pressure.


In the solar thermal business, we call that under pressurization of the tank a "safety seal" accounts for pressure drop when the collectors and piping are outside exposed to ambient temperatures.

The math for proper sizing of a solar thermal tank, get complicated as you calculate a much larger temperature swing for the volume of the system that is outside the building or exposed to the wide ambient to stagnation conditions..

EBEBRATT-Ed

@DIYorBust

Yes. I know of boilers that the heat exchanger is rated for 80 psi and they are shipped wit 40 psi relief valves. Find the ASME tag on the HX. It may be under insulation.

GroundUp

hot_rod said:

Drew_10 said:

I forgot to mention your expansion tanks.
1. I like to set my expansion tanks about 7 to 5 psi below my makeup water pressure setting with a cold boiler. I like to know my expansion tanks are doing work. So if I’m setting up a 22 psi feed pressure, I’m going to adjust my expansion tank pressure to say 17 psi.
2. Also the expansion tanks should be serviceable. I always install an isolation valve for each tank and locate a union or drain valve between the isolation valve and the expansion tank. Give yourself some room to work… they don’t need to be close to each other. It is important to drain the water off of the expansion before checking or setting the tank pressure. You can’t do this in your setup. A tank could have a small leak and you possibly wouldn’t know until water shoots out of the schrader valve. But this could effect the tanks operation. This recommendation and the one I made yesterday regarding the air traps is where I would be looking first.

You will lower the acceptance volume a bit with this method, so if he is close already on expansion space, better not go too low on tank pre-charge pressure.


In the solar thermal business, we call that under pressurization of the tank a "safety seal" accounts for pressure drop when the collectors and piping are outside exposed to ambient temperatures.

The math for proper sizing of a solar thermal tank, get complicated as you calculate a much larger temperature swing for the volume of the system that is outside the building or exposed to the wide ambient to stagnation conditions..

Mmmmm, doesn't less air pressure in the bladder allow more water acceptance in the tank? Maybe we're on opposite sides of the equator, but that's how it works in my neck of the woods.

Larry Weingarten

Hi, I might have two cents for this question If there were no air at all in the expansion tank, it would fill with water but provide no place for water to expand into. So, it seems like the acceptance is reduced as the air pressure is reduced relative to the water pressure, because the available volume of the tank is reduced. Maybe that’s only one and a half cents 🤔

Yours, Larry

hot_rod

Larry Weingarten said:

Hi, I might have two cents for this question If there were no air at all in the expansion tank, it would fill with water but provide no place for water to expand into. So, it seems like the acceptance is reduced as the air pressure is reduced relative to the water pressure, because the available volume of the tank is reduced. Maybe that’s only one and a half cents 🤔

Yours, Larry

Exactly, if the tank is pre-charged to 17 and the fill valve is set to 22, fill water enters the tank until it stabilizes. Youn lose volume before the burner even kicks on. How much? Feel free to use the above formula.

A ripped diaphragm would prove out the same example.


The Wessel and Amtrol calculators allow you to play what ifs with precharge and temperature variables.

I think the concept revolves around Boyles Law. Dan knows the ghost of Boyle well, what say you Dan?

GroundUp

Think here, gentlemen. A combined #30 and #60 have a total tank volume of 12 gallons right? The fluid acceptance volume is only 5.2 gallons, when the pressures are the same- less than half the volume of the actual tanks. Now, obviously zero air leaves zero room for expansion, but that's not what we're talking about here. Dropping the air pressure from 22 to 17 while the system pressure remains 22, absolutely allows more acceptance volume to the tank due to the reduced restriction from the lower air pressure. When pressures are matched, the air volume is more than the water volume. The more you squeeze the bladder, the higher the air pressure rises, which in turn creates more resistance to expansion from the water side. Less air = more space for thermal expansion of the fluid. This is an absolute fact, and I will die on this hill. I didn't believe it either until I actually went ahead and did it. Feel free to perform your own experiment if you wish.

Ya know how domestic water expansion tanks are supposed to be charged to a pressure below the cut-in pressure of the pressure switch? Say 28psi precharge for a 30-50 switch. There is a reason for this.

hot_rod

My tank is pre charged and confirmed at 12psi
I connect it to the system and set the fill at 12 psi
No water will go into the tank, agreed?

Now I push in the schrader valve and allow air out of the tank,  Will  the fill valve open and allow water to enter? You can hear it happening 

Now assume the tank filled 1/2 way with water, my 3 gallon tank now has 1/2 the amount of space to absorb expansion as the water heats. Unless the tank size somehow increased in size you have less expansion space, not more.

Yes or no?

With  a well tank we are not trying to absorb thermal expansion and protect the system from running above a relief setting.

hot_rod

All the tank sizer programs assume the entire system will be at the same temperature, or undergo the same temperature differential.

With a standard boiler running maybe 150- 170, supplying a mixed down temperature to radiant at say 110F. You could in fact downsize the tank a bit, since the entire volume is not seeing that wide delta, from room temperature to 170F for example. Like a solar tank sizer formula, you could split the two volumes and calculate required expansion.

You could also locate the tank up higher in the building. It would "see" a lower static pressure. Less compression of the air so more room for the expansion of the fluid. So once again a smaller tank could be installed.

With the tank properly sized the pressure relief valve would see a pressure 5 psi less than it rating at the highest expected fluid temperature.

GroundUp

hot_rod said:

My tank is pre charged and confirmed at 12psi
I connect it to the system and set the fill at 12 psi
No water will go into the tank, agreed?

Now I push in the schrader valve and allow air out of the tank,  Will  the fill valve open and allow water to enter? You can hear it happening 

Now assume the tank filled 1/2 way with water, my 3 gallon tank now has 1/2 the amount of space to absorb expansion as the water heats. Unless the tank size somehow increased in size you have less expansion space, not more.

Yes or no?

With  a well tank we are not trying to absorb thermal expansion and protect the system from running above a relief setting.

Not agreed. At 12 and 12, the tank absolutely has some water in it. You can literally hear the bladder unsticking from the tank when filling. With less air in the bladder as described, there is more acceptance volume due to lower resistance. I certainly don't mean to be argumentative, but this is a fact. Please feel free to perform your own experiment.

hot_rod

So 4 editions of Modern Hydronics and every tank manufacturer has it wrong?

Its possible to be argumentative and mistaken

neilc

a well tank is a different beast, different operation sequence, from a thermo expansion tank (domestic or heating)

GroundUp

Seeing as nothing on that page nor any manufacturer states that what I said is incorrect, no I am not saying any of them are wrong. You're a tinkerer Bob, feel free to perform your own experiment.

EBEBRATT-Ed

@GroundUp

I think the problem here is and the outcome depends on how the expansion tank is sized. Manufacturers always want to know the relief valve setting and use the difference between fill pressure and relief valve setting to use some of that as pressure rise. For a given system smaller tank more rise larger tank larger rise

Maybe I am missing something but we replace expansion tanks because they have lost there air charge and when they do the relief valve opens.

Had a job in a 4 story building that needed 40 psi to get to the top and they were running the system at 40. But the tank was installed at 15 so they constantly lifted the relief and added MU water.

So it seems to me that air pressure in the bladder below the system pressure basically gives you a smaller tank.

But I can see where under pressurizing an oversized tank may cause less pressure rise in the system but only if the tank is oversized because if it is not oversized it will hit the wall quickly

neilc

A thermal expansion tank needs the air pressure set to match the cold fill pressure or elevation delta of the house or building system.
If you air a tank less than the system pressure, water rushes in and takes up expansion space before the system even starts to heat up, AND EXPAND.
It's written right on the tank, or in the manual.
Over a certain pressure, or building elevation, the tank needs to be certified,
The tank size needs to be matched to, or exceed the system fluid capacity.
Well tanks are different animals.

hot_rod

GroundUp said:

Seeing as nothing on that page nor any manufacturer states that what I said is incorrect, no I am not saying any of them are wrong. You're a tinkerer Bob, feel free to perform your own experiment.

Fig 12 in bright yellow indicates when the tank is pressurized to fill pressure, the bladder or diaphragm us pushed against the nipple. No fluid in the tank obviously.

So the tank has its full volume as acceptance as the fluid is heated.

If I not mistaken you claim 12 psi fill pressure against a tank pre-pressurized to 12, fluid enters the tank?

If so how us that possible, what force allows 12 psi to overcome 12 psi and allow water into the tank?

When a bladder fails, what happens in the system? Do you replace that tank? Why?

Basic Bill Nye science answers that 🙋‍♀️

EBEBRATT-Ed

@neilc

My understanding from a state boiler inspector (at least in MA) that any expansion tank that must operate over 30 psi must be an ASME tank. I don't know if the tank size has anything to do with it

neilc

I wasn't sure of the #, / location,
and tank size doesn't matter

JUGHNE

There is a "dead man" trick to not even have an expansion tank, they would leave the top floor rads with a head of air in them. They still heated enough to do the job.

These were bottom connected supply and return BTW.

I use this in a building with 2nd floor unoccupied rooms. Don't bleed the air out. This keeps the rad from heating fully and wasting energy. The rad valves have small ports to pass water even when fully off. This system does have a full sized exp tank.

This might give you enough extra expansion "tank" on the top floor to see if more "real" tank is actually going to fix the problem.

archibald tuttle

I can't really get a full sense of system piping but I manage a similar system by pumping the secondary to the building on the feed side. thus I can see pressures going up that exceed 30 psi but the boiler(s) actually sees about 26 because of the system loss.

you talk about whether its problematic to let it run at 32 but if it really is at 32 your pressure relief should blow every cycle. although again that goes to the precise accuracy of your gauges and blow off. i assume it maybe has blown off at least sometimes in these cycles or you should check if it is stuck. (and i hate to say but if it is an you unstick it, sometimes they like to drip or they are more ready to discharge and then you might have to replace it)

you should valve off and possibly remove tanks to check that you really have elevated the charge above the system set temperature. when you start to work in numbers this close it isn't so much the number that the gauges say, but whether you observe during a heating cycle from a cold start that the pressure rises relatively directly as the system heats and then stops rising for some time. if the boiler just rises at about the same pace from nominally around 20 psi to a little over 30 psi you are not charged enough on the tanks. you should observe a significant pause at some point between the cold start and the final pressure. if there is enough capacity then the system will not go above that stop point.

that said, what is the temperature control strategy. as @MikeL_2 said, you should be installing enough radiation to get temperatures down. if someone engineered this for you they should at least have given that as a consideration. now that might seem too expensive, but you could still take better advantage if you are really heating a whole 4 story with that navian. i would get an on demand hot water heater (assuming you have enough gas coming into the building to run both and depending on chimney you can get them condensing that can be side vented) and use the setback capability of the navien or an adjunct outdoor reset control and then you won't have to run as hot for as long and usually the highest temperatures are experienced from making domestic hot water because of the exchange losses which means you aren't even condensing when heating cold water nevermind if your return temps are inexcess of 135 for heating, which is just a waste. (i did see some combis at the AHR that claim to have large enough heat exchanger for domestic that they can actually run at a much lower temp to make hot water than most combis and can actually condense but I don't believe that would be true of the way your navien is setup).

If the whole building is on one thermostat you might even consider just constant circulation and ODR which can result in a strategy of using the lowest temperatures possible to keep the building at a constant temp which with this kind of system is potentially more advantageous than setback thermostat. At coldest times you will still reach similar max pressure because you will need pretty hot water temp but i have found this is a nice rational way to run this kind of system. I really like this setup with like twin 140s set up secondary off a primary loop and then if one goes down you still have heat and you just make a habit of checking that neither is off for fault codes so you can fix one before it goes down. If you upsize your DHW exchanger enough you can use a target temp ofr DHW priority that is still in condensing range although the on demands are pretty bombproof.

All of that costs money and care but it sounds like you are spending a good deal of care on the building which is going to pay you back in rents so just rabbiting on here.

good luck

hot_rod

neilc said:

a well tank is a different beast, different operation sequence, from a thermo expansion tank (domestic or heating)

JUGHNE said:

There is a "dead man" trick to not even have an expansion tank, they would leave the top floor rads with a head of air in them. They still heated enough to do the job.

These were bottom connected supply and return BTW.

I use this in a building with 2nd floor unoccupied rooms. Don't bleed the air out. This keeps the rad from heating fully and wasting energy. The rad valves have small ports to pass water even when fully off. This system does have a full sized exp tank.

This might give you enough extra expansion "tank" on the top floor to see if more "real" tank is actually going to fix the problem.

But it really screws up the PONPC , Amtrol talks about this in their engineering guidebook.

EBEBRATT-Ed

Supposed to have 1 tank on a system or multiple tanks connected to the system at 1 location. But in a pinch @JUGHNE trick will get you through a weekend