Help - boiler short cycling on pressure

tobynewman

Hi all--I have a one-pipe steam heating system with 11 radiators spread across 2 floors/apartments. Last winter I replaced the pressuretrol and added 0-5 psi gauge next to it. A few days ago I noticed my boiler making strange noises-when I checked the pressure was at 15 psi! I shut off the boiler and discovered there was a clog in the pigtail going to the pressuretrol and gauge. I cleaned out the pigtail and put everything back together, but now whenever the thermostat calls for heat the boiler will fire up for about 5 minutes, build up about 1.5psi of pressure, and then the pressuretrol causes it to start cycling at roughly 2 minute intervals. This all happens well before any of the radiators start to get hot. Since then I have replaced the vents on all of the radiators, and it hasn't made a difference. I'm not sure whether the mains are vented at all as they aren't accessible at their ends, but I am able to peer in at them from about 3 feet away at either end, and from my limited vantage point I'm not able to see anything that looks like a vent.

I want to be clear that I'm not completely sure whether this was an issue before the incident with the clogged pigtail. My recollection is that the boiler used to fire continuously until all the radiators were hot, but I could be wrong. As of now all the radiators do eventually get hot and satisfy the thermostat, but I'm worried that the constant cycling is bad for the boiler and consuming excessive gas. Any help would be appreciated--thank you!

KC_Jones

Pressure in a steam system is a function of boiler size, to the system and venting mixed in. So if the system can't take the steam volume being produced, pressure builds and it's cut off by the pressuretrol (pressure safety) to prevent over pressurizing. If you have no main vents, you need them, especially since you say you don't even have the main filled with steam when it starts cycling, main vents would help that situation. After the main venting is squared away you can move onto balancing the radiator venting.

That said, if the boiler is oversized, you are only going to get so good with this and may have to live with cycling.

I'd speculate that boiler is massively oversized based on your description of how it's running. If you want to determine this (and I think it's worthwhile), need to measure all the radiators and calculate the EDR for the system, then compare that to the nameplate on the boiler. If you decide you want to do that, let us know and we can offer some guidance on doing it. Hint: it's not hard at all.

The boiler piping looks ok, but without a make and model can't be 100% sure. Would need to verify their recommendations for that size boiler with respect to outlets and pipe size. If you are curious about that, post up the make and model, or just a picture of the nameplate would do.

nde

If it locks out on pressuretrol at 5 minute mark from cold start something else is wrong besides oversizing as that is not enough time for steam to even be produced. That old header looks huge so perhaps you have a large EDR load. Nevertheless it sounds like there could still be a clog in the pressuretrol pipe run vs the pigtail.

If this is 1 pipe, then trace the mains from the boiler, at the point near where each main (looks like you have 2) drop down from ceiling to become returns is where you want your main vents. If lacking that is definitely something costing you lots of wasted fuel and will often cause cycling on pressure, But again it usually takes 15-20 minutes for such a scenario to occur so I would look to pressuretrol still being clogged.

EdTheHeaterMan

Hi all--I have a one-pipe steam heating system with 11 radiators spread across 2 floors/apartments. Last winter I replaced the pressuretrol and added 0-5 psi gauge next to it. A few days ago I noticed my boiler making strange noises-when I checked the pressure was at 15 psi! I shut off the boiler and discovered there was a clog in the pigtail going to the pressuretrol and gauge.

Quite possible the pigtail was partially plugged last winter when the new control and gauge were added. that would explain longer run times due to the slow migration of pressure into and out of the partially plugged pigtail.

With the completely plugged pigtail, you had to inspect it and completely remove any blockage. Now it is seeing the actual pressure in real time. This does not help you solve the short cycling, it is just an explanation for what may have happened that changed the operation timing. Adding main vents and getting the rad vents dialed in will get the air out faster and perhaps reduce the short cycling, at least up to the time when all the rads are hot.

tobynewman

Thanks everyone for your help!

KC_Jones said:

I'd speculate that boiler is massively oversized based on your description of how it's running. If you want to determine this (and I think it's worthwhile), need to measure all the radiators and calculate the EDR for the system, then compare that to the nameplate on the boiler.

The boiler is a New Yorker CGS60A, which puts out 143000btu. I just calculated an EDR of 260 for all the radiators, so if I'm dong my math right the boiler is oversized by a factor of 2.29. I'm new to this but that does sound like a lot. I will admit that I have shut off three radiators downstairs in an attempt to balance the heat (I did not include these in my EDR calculation). This was after switching all the upstairs vents to Maid O Mist #Ds and all the downstairs vents to #4s, and still having it get much hotter downstairs.

My calculation didn't include any piping losses. I believe most of the piping is uninsulated--my basement is heated entirely by the uninsulated mains and it is usually the hottest part of the building.

nde said:

If this is 1 pipe, then trace the mains from the boiler, at the point near where each main (looks like you have 2) drop down from ceiling to become returns is where you want your main vents. If lacking that is definitely something costing you lots of wasted fuel and will often cause cycling on pressure, But again it usually takes 15-20 minutes for such a scenario to occur so I would look to pressuretrol still being clogged.

I agree it's a very short amount of time to build pressure, but if the pressuretrol is still clogged how would that lead to cycling on pressure? When the pressuretrol cuts in and out the readings on the adjacent pressure gauge always seem to match.

EdTheHeaterMan said:

Quite possible the pigtail was partially plugged last winter when the new control and gauge were added. that would explain longer run times due to the slow migration of pressure into and out of the partially plugged pigtail.

This is a very real possibility that I didn't think of until now!

It sounds like a solid first step will be to open up the ceiling in my basement, determine once and for all whether the mains are vented, and add vents if necessary. Beyond that, should I talk to a professional about under firing the boiler? Or should I basically ignore the short cycling at that point with the intention of someday getting a better-sized boiler?

Thanks again for all the help!

KC_Jones

If you are closing radiators, then you definitely have a balance issue. Balancing starts with proper main venting. Once that's done you can turn all radiators on, and leave them on, then get the radiator venting proper. You will probably end up with much smaller vents upstairs once you get the main venting squared away. #4 on the first floor may end up being good.

Shutting down 3 radiators is exacerbating the problem, probably dramatically. Add up the total system EDR for comparison since you should be running with them all on.

The current version of that boiler is rated for 446 square feet of radiation and that number is accounting for the 33% pick up factor in that the full boiler output isn't in that number, so you can get an idea how dramatically oversized you are.

According to current manual your piping meets minimum spec, header actually exceeds as it appears to be 3" so I don't see the piping as being any part of your issue.

Jamie Hall

I doubt that you have a pressuretrol problem at this point. You do have a major oversizing problem with the boiler, and it is unlikely that it can be downfired enough to really make much of a difference. It is what it is.

But -- you do have a venting problem. Even though the mains are relatively short, perhaps, I would recommend that you go with at least one Gorton #2 on each main. If you have access to the tops of the risers going to the upstairs radiators you might also look at adding a Gorton #1 to the top of each riser. Then start working on the radiators (and open those three you shut off). Start with the Maid-O-Mist 4s downstairs, and the Ds upstairs as you have them. The Maid-O-Mist 4 is about as slow as you can go easily, although the Hoffmann 1A set at 1 is a little slower. They're harder to set, though.

mattmia2

You may have mains that continue up in to the apartments somewhere and the main vents might be in an apartment, especially in the top floor bathrooms or kitchens.

Fixing the main vents will make the balancing easier. Perhaps you can open up the currently turned off radiators once you can get the air out.

Since it is a multifamily building it should probably have a separate pressuretrol with a manual reset on a separate pigtail.

The riser out of your boiler looks very small for that size of a boiler and that horizontal section before it gets to an old header that was reused will hold water and cause problems with water hammer and delayed steam production but I'm not sure how much that is contributing to your problems.

ethicalpaul

Something is very weird if 4 "D" vents can't let steam come in vs #4 vents. Those 4 "D" vents are more than a Gorton #2. Something is weird.

TonKa

It may prove fruitless, but it might be worth checking if you have more radiators shut off than you currently think you do. If they're not venting and getting hot, it'll only exacerbate the problem further.

tobynewman

Thanks again for all the suggestions. I opened up the ceiling in my basement earlier and discovered a few things. There are actually 4 mains--two running next to each other in either direction from the boiler. I'm not sure but I think it may be one dedicated main for each floor. The two mains running to the front of the building have vents, but they look pretty old and I don't feel any air escaping from them when the boiler builds pressure. The two mains at the other end of the building both have plugs where the vents would have been. One of those is at a 45 degree angle too--I don't know if that will cause issues with a vent that's meant to be vertical. Photos below. I may get a plumber involved if I can't loosen these myself. I would love any vent suggestions based on the above.

In terms of balancing the system once the mains are vented, it's worth mentioning that the downstairs apartment has been renovated much more recently, rooms have been combined and at least some of the exterior brick walls are insulated. Upstairs is still divided into many smaller rooms, each with their own radiator, and none of the exterior walls are insulated. The attic above actually is insulated, but that's still heat escaping through the roof that the first floor apartment doesn't have to contend with. My theory is that the downstairs apartment actually has a much lower heating load that it did possibly when the boiler was sized. This may be contributing to me feeling like turning off a few radiators downstairs is the only way to keep that apartment from getting uncomfortably hot. With all the rads on, the downstairs apartment stays 7-8 degrees F hotter than upstairs. With the three downstairs rads turned off, that difference shrinks to 2-3 degrees. I know it's not great for the boiler to be short cycling all the time, but I would also rather not have to resort to opening the windows to regulate the heat downstairs!

mattmia2

Are the vents cold when there is no air venting from them?

The one with the 45 should have another 45 at or near the vent to get it vertical. It would be better to put very slow vents on all of the first floor radiators than to shut some of them off. TRVs at the vents to stop the radiator from venting at the beginning of a cycle if the room is already warm enough is another option.