New boiler installation running very hot and reaching pressure quickly

jmerrill · February 25

I just replaced a boiler on a two pipe steam system and it reaches steam pressure very quickly probably under 5 minutes. The water level in the gauge glass starts to drop as well. I set the pressuretrol to .5 and 1 on the differential. I checked gas pressure and it is not overfiring. Boiler was skimmed multiple times over multiple days. I used a thermal imaging camera and the steam leaves the boiler very quickly. I also replaced the main vent. The main vent seems to vent after running the boiler for a short period of time. Any thoughts or feedback would be appreciated.

ethicalpaul · February 25

Was the boiler sized correctly? It sounds like it is oversized and lacking good pressure control as well.

The water level could be dropping simply due to the pressure (water getting pushed out the back of the boiler to the wet return). Do you have a low pressure gauge on there to see what the pressure is getting to?

Jamie Hall · February 25

I'd be delighted if my boiler made steam quickly. I'd not be delighted, however, if it reached 1 psig or so quickly, or worse if it shut off on pressure before my radiators were nice and warm.

Which leads to two questions. First, how was the boiler sized? Was it properly matched to the radiation which it is powering? There's only one way to do it right with steam…

Second, what is your main venting like? You say replaced it? With what vent? How big is the system it is venting?

jmerrill · February 25

The existing main vent was a hoffman no.75 which was replaced with the same. The replacement boiler is a 200,000 btu boiler. What would cause the issue oversizing the boiler or undersizing? Cant really speak on who sized the old to the new since I am just the installer.

ethicalpaul · February 25

OK you are the installer…that's good to know. How did you choose the size of the boiler you installed?

jmerrill · February 25

Did not choose it just stuck here trying to figure it out.

ChrisJ · February 25

https://forum.heatinghelp.com/discussion/comment/1889573#Comment_1889573

My guess is he works for a company who sold a boiler, and he was simply sent out to "get it done".

He's asking for help which, I think is a big plus.

@jmerrill Is this a single pipe system? What main vents are there? What radiator vents?

ethicalpaul · February 25

I can think of several bigger pluses…but in any case he said it’s a 2-pipe

dabrakeman · February 25

So someone else took the old boiler out and you installed the new boiler? Sorry just trying to understand the situation. Assume it must be a pretty big house since a 200k btu boiler would be good for about 625sqft of connected radiators. I would also be very surprised if a single Hoffman 75 is enough main venting on a system that size but we would need to know the lengths and pipe sizes of the pipes being evacuated of air by the steam. It would be great if you could provide some more information.

Do you know what size boiler was removed?
Are you certain all the radiator valves throughout the house are fully opened and someone before you had not shut some off for some reason?
Provide pictures of the installed boiler from a distance at a few different angles.
Provide a photo of a typical radiator in the house

pecmsg · February 25

thumbs up for coming here and asking.
now you need to start getting us information.

EDR radiators in the building?
Pictures of the boiler ID tag.

pictures of the new boiler piping.

Jamie Hall · February 26

Just to clarify — if a boiler is oversized, it will produce more steam than the system can absorb. This is what makes the pressure rise — and why we are a bit suspicious that it may be oversized.

Not much to be done about it…

As others have said, that Hoffman 75 is an excellent vent. It's also not big enough, pretty much no matter what the main lengths are. You might get away with just swapping it out for a Gorton #2 for that size boiler.

Captain Who · February 26

https://forum.heatinghelp.com/discussion/203956/new-boiler-installation-running-very-hot-and-reaching-pressure-quickly

Do you mean to say "The main vent seems to close after running the boiler for a short period of time" ?

If you have thermal imaging camera what is happening at the radiators when the boiler shuts off on pressure (presumably since you don't have low pressure gauge)? Maybe the steam traps can't handle the volume of air that this boiler that may be oversized is able to push out of the radiators? How far across are the radiators filled with steam when the boiler presumably shuts off on pressure?

4GenPlumber · February 26

Near Boiler pics are the most important. Is there a hoffman differential loop?

Jamie Hall · February 26

https://forum.heatinghelp.com/discussion/comment/1889682#Comment_1889682

Oh dear I hope not. If there is, the system was designed to run on less than half a pound pressure differential between the mains and the dry returns, A low pressure vapourstat will be needed to control the boiler, and if the boiler is seriously oversize it may be necessary to use a time delay relay to prevent excessively short cycling — there are numerous threads on The Wall about that, and it's very much a kludge to fix a mistake, but sometimes you have to run what you brung.

ChrisJ · February 26

What is the reason guys can no longer downfire atmospheric boilers by removing burners?

They used to do it all the time years ago, what changed?

New boiler installation running very hot and reaching pressure quickly

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