no pressure gas fired steam boiler

Bill Winch

I have a 1930 house in NJ, 3100 sq ft, with a gas fired boiler and one pipe radiators. The gas bill for November was $410 and I am trying to help the tenants lower their bill. The boiler is about 10 years old and I recently replaced all the radiator and main vents.

When the thermostat is calling for heat, the flame stays on continuously and there is no pressure on the gauge even if I set the thermostat to 80 and the heat is on for two hours. All the radiators get hot and but the vents on the radiators furthest from the boiler are cold.

Does no steam pressure mean that there is a steam leak in the system? If so how can I find it? Could the boiler be undersized? I ordered a 0-5 psi gauge to replace the 0-30 psi one I have to better see if there is any pressure developing. The pressuretrol is set for 1/2 psi cut in and 1-1/2 psi cut out, but as I said, there is no pressure developing and it seems like the flame eventually shuts off when the thermostat stops calling for heat and not because the pressuretrol shuts it off on high pressure.

I was thinking of shutting off all the radiators and seeing if pressure builds then. Any thoughts on how to troubleshoot?
Thanks.

Brad White_191

Questions, Bill

Hi Bill

You say that all of the radiators are hot but the vents are cold? I mean, if the radiators are hot, that is the goal. That the boiler runs continuously is incidental to making pressure for if the radiators are all hot, there is sufficient pressure to do that.

Setting the thermostat will not affect system pressure (beyond enabling it), but just set the space temperature target.

Now, if it takes two hours, is that to heat the building or get the radiators hot? How long does it take to get the radiators hot in the first place? If 15 minutes, that sounds great. If the first hour is spent warming the system, I would suspect a leak. (Look for any really white steam out your chimney as an indicator of a leak above the waterline.)

If you do suspect a steam leak, I would ask what your make-up water rate is. Do you have a metered feeder or a record of how often you have to restore the boiler water level?

Random drive-by thoughts.

Brad

Wethead7

questions

Is the piping insulated?
Is water on the floor or any other place?
How much water is it using?
When was the last time it was serviced?

Mike

Bill Winch

reply to questions

Thanks for the thoughts. I have only had the house since Jan 08. When I first operated the system, two of the radiators furthest away from the boiler did not get hot at all. After insulating the pipes in the basement, both of the far away radiators get hot, but are the last ones to heat up and do not always heat all the way across.
I have an automatic water feed and don't manually add water, but I have no idea how often the automatic feeder comes on. Seems like it would be good to get a feeder which records the amount of time it has been on. I guess that would tell me if there was a leak? I have not seen any water on the floor. As for servicing, I just had a clogged pigtail replaced. I asked the technician what other service should be done on the system, but he did not recommend any. It seems like cleaning the burner and the inside of the boiler would be a good thing?
Most of the radiators get hot in about 15 minutes with the ones furthest away from the boiler taking about 25. The two radiators furthest away from the boiler do not get hot all the way across to the vent.
It seems like there is no pressure in the system which makes me think either there is a leak or the boiler is undersized. Even if I crank up the thermostat 10 degrees and the flame is on continuously for two hours, I still see no pressure on the gauge and when I put a little liquid bubble over the radiator vent hole it looks like there is no pressure, or even a vacuum.
Please correct me if I’m wrong, but I thought the flame boils the water, steam pressure develops, pushing the steam towards the open vents causing them to close as they get hot, then the steam goes to vents still open, and once these vents close, the pressure builds until the high pressure cut-off shuts off the flame. When the heat is removed, the pressure drops until the low pressure cut –in turns the flame back on, and this continues until the thermostat setting is reached. This is the way I understand it should work, but again; please tell me if I do not understand it correctly.
Thanks again for your input

nicholas bonham-carter

missing pressure

you should only need 3 ounces of pressure to fill your system with steam, and close your vents.

with steam, less pressure "is the new more".you will have problems if your vents are not functioning properly, [and spend much more money on fuel!]

my advice is to increase your venting capacity with either hoffman or gorton. get one of the largest for each main.

also get a good low pressure gauge [gaugestore.com 0-5 psi.] you will then know how your system is running pressure-wise.--nbc

Jamie Hall

fundamentally, Bill

you are on the right track... sort of. When the boiler fires up, steam is evaporated (boiled). As Nick notes below, 3 ounces is plenty of pressure -- and you'll not see that on any gauge.

What happens next, though, is that the steam rushes out to the radiators, displacing the air through the vents (so the bigger the vent, the faster a radiator will heat). When it gets to the radiator, though, it promptly condenses -- heating the radiator. The only time pressure will actually build in a system is once all the radiators are pretty well hot across, and all the vents are closed. Then pressure may build; how fast depends on how much radiator you have vs. how much fire you have (how much steam is being made). It is quite possible in a system which is sized 'just right' that pressure won't build at all!

The thing you were missing is the steam condensing in the radiators...

It does sound as though improving the venting might help those two slower radiators.

It also sounds, though, as though the whole thing may be slightly undersized. You mention a two hour run time. Unless you are recovering from a big setback, or are working with a very cold day out, I wonder a bit whether you are getting enough heat! If a system is just maintaining the house temperature, a properly sized one really shouldn't run more than 30 to 40 minutes every couple of hours...