Short cycling steam boiler, many possible issues

TDatta

Hello all, I have been reading the discussions here for a while, and trying to figure out what's wrong with my system. Ive learned a lot from what I have read, but I have some specific questions.

Here is the background. Bought a house (1930s) recently. It has an oil boiler (Peerless ECT-04), with a Riello Burner (F5). The two main symptoms are:
1. System uses a lot of fuel, last year they used 1300 gallons of oil according the oil supplier. (NY-Long Island)
2. Boiler short cycles a lot after heating up (5 min on, 5 min off, before I made any changes).

My investigations have yielded the following findings:
A. I've calculated the EDR*240 to be about 60,000, there is also a tankless water heater (was set at 160f when I looked at it). From what I can find, this boiler has an output of 151 MBH (this is what I assume since it has a F5 boiler, there are other versions of the ECT-04 that have up to 208 MBH, but they require an F10 burner). So 60000+40000 including tankless heater comes to 100,000 BTU and the system is spec'd to 151,000 BTU. So its oversized by 50%.
B. From cold, the radiators get hot in about 20 minutes.
C. I can only find one main vent in the boiler room, and it doesn't seem to be working well. There are two mains coming out of the boiler, the one with the main vent that I am talking about takes a long time to heat up. The other main heats up fast but I cant find the vent, the basement is fully finished.
D. The pressuretrol is what is causing the cycling, this is my assumption. There is a Nest thermostat which is complaining about loss of power every time the cycle is off. So I assume its not the thermostat that is causing the cycling.
E. Water level is correct, low water shutoff works, auto feed works. Water level does not bounce during operation.
F. Water was super dirty. I have flushed it about three times over the last month, its still a little dirty but much clearer. Flushing the water seems to make no difference to the short cycling.
G. The 30 PSI gauge is completely off, it used to read up to 20 PSI, contractor came and cleaned out pigtail and inlet of gauge, pressures still off, but it doesn't read as high any more.

I changed the following things:
1. Pressuretrol was at 1 PSI cut in and differential of 2. I have changed that to .5 cut in, and differential of 1.25.
2. Changed aquastat to 150f from 160f.
3. Radiators used to make a lot of noise, I replaced all the vents with Hoffman 40 variables. Noise is much reduced now.

The effect of changing the pressuretrol settings is that now the short cycling is worse just under 4 mins on, and 4 mins off after initial long burn (25 min) on call for heat. I cant trust the gauge so I started measuring temps at the radiators and at the boiler. Radiator temp max ranges from 226f to 236f among the radiators. The boiler main temps range are 226 on the slow venting main and 236 on the fast venting main. Boiler cuts off when the hotter main temp reaches 236, boiler turns back on when the hotter main temp drops to
225. According to steam charts this corresponds to pressures of 4 PSI to 8.5 PSI, which is much higher than what the pressuretrol is set at.

What should my next step be? New pressuretrol or vaporstat? Will that help with such an oversized boiler?

Thanks in advance.

neilc

so by your numbers you have a boiler that is over twice what you need,
and that is gonna short cycle.
Is the house comfortable?
any hammering or hissing?
you should add a known good low pressure gage,
keeping the junked 30 to satisfy the authorities.

TDatta

No hammering. I don't know what hissing I should be looking for. The radiators don't hiss. Except for one which is an in wall, and I think the hissing is actually from the inlet which is painted over and I cant move the valve.

House can get comfortable, I suspect the radiators are undersized for the house. I tried overnight setbacks of 5 degrees and it takes more than two hours to come to temp.

I am thinking of adding a good low pressure gauge. But based on the temperatures I recorded it seems the pressuretrol is not working properly .5-1.75 PSI is actually 4-8.5 PSI based on temps.

My thought is that the system is just burning a lot of fuel to get the high pressures, and that the house is not benefiting from the extra burn.

Jamie Hall

With a boiler that wildly oversized, it's difficult.

First off, on sizing -- the tankless water heater is never included in boiler sizing, unless the hot water demand is much higher than a typical residential setting. That ECT-04 has a rating of 471 square feet; back converting your BTU figure it appears that your system EDR is around 250 square feet. Even if it has been downfired some, it is, as you say, at least 50% oversize. Your cycle timing points in the same direction.

This can't be helped. The boiler is what it is.

So... what needs to be done. First, if your temperature readings are correct (is this an IR thermometer or a strap on? IR thermometers are affected -- considerably -- by the condition of the target), you are way over pressure. For that, I suggest that you remove the pigtail to the pressuretrol and make sure that it is clear, and the opening to the boiler is clear, and then put it back -- adding a good low pressure gauge (0 to 5 psi) at the same time. This will allow you to be sure that the pressures are in the range you want -- 0.6 psi cutin to 1.6 psi cutout.

That won't help the cycling, but will help your vents to live to see another day.

Then on the main with the vent which may -- or may not --be working, replace that with a Gorton #2. Try and find the other vent -- it's likely there somewhere -- and replace that too.

That won't help the cycling either, but will slightly increase your efficiency.

You don't mention whether the mains are insulated or not -- if they aren't, insulate them. 1 inch fibreglass is preferred.

None of this will reduce your fuel bill that much -- perhaps as much as 5%, but it's unlikely to be more -- as your fuel bill is primarily determined by how much heat is needed, and a BTU is a BTU.

Now. To go back to the cycling. With a boiler that much oversize, some of us have had good success with using a timer to extend the off time of the boiler, once it shuts off on pressure. There are various ways to do this -- some simpler that others -- but it has the virtue of keeping the boiler running longer, when it does run. @PMJ has really been the pioneer in this -- you could send him a PM -- but others have worked with it as well.

TDatta

Jamie Hall said:

So... what needs to be done. First, if your temperature readings are correct (is this an IR thermometer or a strap on? IR thermometers are affected -- considerably -- by the condition of the target), you are way over pressure. For that, I suggest that you remove the pigtail to the pressuretrol and make sure that it is clear, and the opening to the boiler is clear, and then put it back -- adding a good low pressure gauge (0 to 5 psi) at the same time. This will allow you to be sure that the pressures are in the range you want -- 0.6 psi cutin to 1.6 psi cutout.

IR thermometer corroborated with FLIR camera with emissivity correction and also corroborated with surface thermapen. Contractor came by and cleaned out pig tail to pressuretrol. I will call them back and ask them to install the new gauge once I get it.

Jamie Hall said:

Then on the main with the vent which may -- or may not --be working, replace that with a Gorton #2. Try and find the other vent -- it's likely there somewhere -- and replace that too.

Ive looked up and down for the other main vent. Cannot find it. I will try to replace the main vent but I cant put on a Gorton #2 because of how close it is to the wall. I need something with a smaller overall diameter. Image of vent attached.

Jamie Hall said:

You don't mention whether the mains are insulated or not -- if they aren't, insulate them. 1 inch fibreglass is preferred.

The mains were partially insulated. The hotter one was mostly insulated after it splits from the header, the colder one was not insulated and I cant see what happens when it goes into the wall. I started insulating as much as I could with 1.5" fiberglass last week. Images of partial install attached.

Jamie Hall said:

Now. To go back to the cycling. With a boiler that much oversize, some of us have had good success with using a timer to extend the off time of the boiler, once it shuts off on pressure. There are various ways to do this -- some simpler that others -- but it has the virtue of keeping the boiler running longer, when it does run. @PMJ has really been the pioneer in this -- you could send him a PM -- but others have worked with it as well.

I've been reading about this. This appears to be a good solution. I think there are two ways that I can do this. One, based on pressure, hit a pressure, relay off for a set amount of time. Second, put something inline to force the Nest to limit continuous call to 20 minute burns (or something similar), with forced dead time of 20 minutes in between.

Jamie Hall said:

None of this will reduce your fuel bill that much -- perhaps as much as 5%, but it's unlikely to be more -- as your fuel bill is primarily determined by how much heat is needed, and a BTU is a BTU.

Doesnt some of the energy input get wasted driving up the pressure? Or is it that the higher pressure comes with higher temperature which eventually goes into the house?

Jamie Hall

Some of the energy does get wasted driving up the pressure -- so there will be some gain there. As you note -- most of it winds up somewhere, though.

On the cycle control -- the first approach (hit a pressure, shut of and force a delay) is simple and works well. Another approach -- a little more complex -- is to have a thermostat at the farthest end of a main or on the last radiator (preferable); when it hits steam temperature, turn the boiler off for a fixed time.

Nests and steam are very problematic. The Nest was never meant to control steam heat. You need to turn off all the learning and "smart" features and limit the setback, if any is used at all, to 3 degrees. If it is connected with only two wires (power stealing) it will give you endless trouble.

On the vent. They didn't make it easy, did they? Go up with a short nipple to a union. Another short nipple up, 90 over, 3 inch nipple, 90 up, Gorton. Problem solved.

TDatta

What about the pressuretrol? It is wildly inaccurate. Do you think I would be better off with a new one or a vaporstat?

Jamie Hall said:

On the cycle control -- the first approach (hit a pressure, shut of and force a delay) is simple and works well. Another approach -- a little more complex -- is to have a thermostat at the farthest end of a main or on the last radiator (preferable); when it hits steam temperature, turn the boiler off for a fixed time.

Im going to look into both options. Electronics is my field and I could go for the second option. But it seems that the first may be simpler except that I need to tap into the pressure. But what about another thermostat like a honeywell where I can limit the CPH? Would that work the same way?

Jamie Hall said:

Nests and steam are very problematic. The Nest was never meant to control steam heat. You need to turn off all the learning and "smart" features and limit the setback, if any is used at all, to 3 degrees. If it is connected with only two wires (power stealing) it will give you endless trouble.

Yes, its connected with two wires, its a pain, always complaining about no power when the pressuretrol cuts off.

Jamie Hall said:

On the vent. They didn't make it easy, did they? Go up with a short nipple to a union. Another short nipple up, 90 over, 3 inch nipple, 90 up, Gorton. Problem solved.

Thank you. I will look into getting these parts and ask the contractor to put them in when I call them. Im a bit concerned with the age and rust. Can I trust this old vent and the threading that its in to not fall apart?

PMJ

I agree with @Jamie Hall that efficiency gains are not going to be dramatic just by eliminating occasional pressure spikes. The primary driver for all of my work has been comfort. Filling these systems up enough to bounce a couple times off the pressure limit is overshooting the temperature setting period. Some people really don't mind (or may even like) roaring hot radiators and then longer waits while they basically go back to room temperature. I really didn't like that and set about evening things out. Just a few more controlled cycles produced just steadily gently warm radiators a much higher percentage of the time. Much more like how it was originally intended. If your system is well balanced, the timer setup is inexpensive and easy to do.

Eliminating air handling altogether with vacuum really did change the efficiency and comfort more significantly. But I realize that is out of reach for most folks.

I'm happy to help out anyone who wishes to try a timer and/or 2 pipe vacuum.

dabrakeman

@PMJ In a recent thread you mentioned the TR-6512U which basically sets a max burn time and once hit a min off time. Simple and logical but subject to some variation between normal operation and recovering from setback because can take much longer to build steam from completely cold boiler. How would you (or @TDatta) propose to tap pressure (something low like 0.25-0.5psi) to trigger the off then start the time delay to refire? The purely time based method is nice since only a single add on unit is needed to do everything.

Jamie Hall

As a first pass on tapping the pressure and trying the time gambit -- if you can get the pressuretrol to work at 1.5 psi, use that signal. It's higher than you either want or need, but as a way to try the concept without spending much money...

PMJ

dabrakeman said:

@PMJ In a recent thread you mentioned the TR-6512U which basically sets a max burn time and once hit a min off time. Simple and logical but subject to some variation between normal operation and recovering from setback because can take much longer to build steam from completely cold boiler. How would you (or @TDatta) propose to tap pressure (something low like 0.25-0.5psi) to trigger the off then start the time delay to refire? The purely time based method is nice since only a single add on unit is needed to do everything.

@dabrakeman, my recommendation is to use the timer to avoid pressure altogether. The timer control at its simplest will be slower to get started from a dead cold start as you observe. Your suggestion is to only use the timer after a pressure condition is reached. This is possible, the wiring more complicated. I have never drawn that one up, but would consider doing so. I will say that I ran several years with the simple timer setup and slower dead cold startups. An extra half hour on the relatively few dead cold starts is not as bad as you might think. Bear in mind that when you actually need heat, there are few of those.

I would recommend instead considering the installation of a remote temperature switch and use it to cover the cold start problem by energizing the TR-6512U only after steam has first reached a remote location. This way you can control your cycles from the same fill level without any pressure ever.

nicholas bonham-carter

Replace that main vent with some Gorton #2’s, before fiddling with the timers and such.—NBC

Gsmith

And find the main vent for the other main, or add one at an appropriate place. Importance of main venting cannot be over emphasized.

TDatta

PMJ said:

I agree with @Jamie Hall that efficiency gains are not going to be dramatic just by eliminating occasional pressure spikes. The primary driver for all of my work has been comfort. Filling these systems up enough to bounce a couple times off the pressure limit is overshooting the temperature setting period. Some people really don't mind (or may even like) roaring hot radiators and then longer waits while they basically go back to room temperature. I really didn't like that and set about evening things out. Just a few more controlled cycles produced just steadily gently warm radiators a much higher percentage of the time. Much more like how it was originally intended. If your system is well balanced, the timer setup is inexpensive and easy to do.

Eliminating air handling altogether with vacuum really did change the efficiency and comfort more significantly. But I realize that is out of reach for most folks.

I'm happy to help out anyone who wishes to try a timer and/or 2 pipe vacuum.

Very interested to learn about the applications of vacuum in this.

Jamie Hall said:

As a first pass on tapping the pressure and trying the time gambit -- if you can get the pressuretrol to work at 1.5 psi, use that signal. It's higher than you either want or need, but as a way to try the concept without spending much money...

Im going to test the pressuretrol myself and see if it needs to be replaced. I can generate known pressures at work, just need to find the fittings.

dabrakeman said:

@PMJ In a recent thread you mentioned the TR-6512U which basically sets a max burn time and once hit a min off time. Simple and logical but subject to some variation between normal operation and recovering from setback because can take much longer to build steam from completely cold boiler. How would you (or @TDatta) propose to tap pressure (something low like 0.25-0.5psi) to trigger the off then start the time delay to refire? The purely time based method is nice since only a single add on unit is needed to do everything.

There are some other discussions with posts on pressure switches with the right fittings. Im looking at the data sheet for the delay timer, its not clear to me yet if what you describe is possible with just a pressure switch and the delay timer. I need to look into it a bit more.

nicholas bonham-carter said:

Replace that main vent with some Gorton #2’s, before fiddling with the timers and such.—NBC

Im going to ask the contractor to do this. I dont trust myself with those rusty threads.

Gary Smith said:

And find the main vent for the other main, or add one at an appropriate place. Importance of main venting cannot be over emphasized.

I just did another search, this time I followed the main down to the other end of the house. Its all covered up in dry wall. The vent has to be behind the wall. Otherwise I dont know where it could be. But this line vents fast, though it could be the two new Hoffman 40s i put on the radiators that line feeds.

PMJ

It is important to understand that the timer method requires first a properly vented and balanced system. I am not suggesting in any way that it is a "cure" for problems in those areas.

Having said that though, I must also point out that the fundamental issue the timer method improves is not a venting issue and cannot be fixed by improved venting. That issue is the inherent delay in these systems between the supply of steam and the reaction at the Tstat because air is not being mechanically circulated. These systems were originally designed to be continuous steam where no such delay existed.

The absolute smallest boiler possible for a given system is still producing steam at at least 2 times the rate required to cover the heat loss on an average day. Even with perfect venting that boiler will still overfill and then overshoot the target temperature after the tstat has finally reacted. It may be a small amount and quite acceptable to most people. For those of us who prefer radiators to be just comfortably warm most of the time rather than have much bigger oscillations, some sort of burn time/wait time control is required.

So even heat and comfort is the primary reason for the timer; that it also eliminates the possibility of pressure short cycling is a side benefit, not at all the primary purpose.

One final note. The reason I know that venting cannot cure the primary issue I am addressing is because even in my vacuum system the timers are required for the same reason above. And in the case of the vacuum system there is next to no venting required at all, so clearly it cannot be the solution to the problem.

TDatta

PMJ said:

One final note. The reason I know that venting cannot cure the primary issue I am addressing is because even in my vacuum system the timers are required for the same reason above. And in the case of the vacuum system there is next to no venting required at all, so clearly it cannot be the solution to the problem.

Could you describe more about your vacuum system or point me to where I can read about it. Just curiosity at this stage.

PMJ

There are bits and pieces in a lot of places on the site but probably nothing comprehensive in one place. Perhaps I should start work on a write up.

It is terribly simple in 2 pipe. I have a Mouat vapor system. I removed the single vent on the dry return and replaced it with a single 1/2NPT 24vac solenoid valve because it has no cracking pressure so zero resistance to air leaving when open. I installed an ultra low pressure switch to tell when the system pressure gets to atmospheric and I open the solenoid valve at those times at the end of each burn. The valve closes the instant the burner goes off and then the system sinks into vacuum between cycles.

Attached is a 12 hour plot of the system pressure. The peaks at the top are at 0 pressure and each are about 4 minutes in duration. So the system ends up open to the atmosphere about 10% of the total time. The space in the middle is a setback.

Anyway, I'm happy to discuss any time - here or PM.

Jamie Hall

@PMJ is absolutely right: you have to get the venting and distribution right. You also have to get the boiler power adjusted to the system demand. He is working much more with the boiler power half of the pictured -- but you have to have both halves correct to get the good, even heat that steam can provide.

It's not that hard -- but you have to consider the whole picture.

And yes, @TDatta , it may very well be that those Hoffman 40s on the last radiators on that line are acting in part as main vents for that line. Nothing seriously wrong with that -- provided that those radiators aren't putting out too much heat.

TDatta

One main being colder than the other is a sign of imbalance. Im going to install some larger vents on two of the radiators that it feeds to increase venting. I need to wait for the contractor to come out to change the main vent since Im concerned about breaking it.

With regard to timing and adding delays. What if I were to ditch the nest and use a Honeywell with programmable CPH and set those to 3?

PMJ

TDatta said:

One main being colder than the other is a sign of imbalance. Im going to install some larger vents on two of the radiators that it feeds to increase venting. I need to wait for the contractor to come out to change the main vent since Im concerned about breaking it. With regard to timing and adding delays. What if I were to ditch the nest and use a Honeywell with programmable CPH and set those to 3?

If you truly have an imbalance I would get that fixed and see where you are before doing anything else.

Jamie Hall

"With regard to timing and adding delays. What if I were to ditch the nest and use a Honeywell with programmable CPH and set those to 3?"

That would probably help a lot.