Home hot water heating!! 1

[sznic]

Hi,
I have a problem with my home's heating system. It is hot water heating with gas boiler. Problem I have is that when thermostat is calling for heat and gas boiler is on, system overpressurise causing reliefe valve to open, actually it only lets out few drops of water. System has a bump tank located by joyces. Had that problem before, maybe ten years ago, heating guy came and fixed it, however I forgot what he did. Anyone out there that could help ??? Thanks.

 

[quark]

There may be some debris (or rusting) between relief valve disc and seat. Just clean it.

Regards,

 

[TBP]

The expansion tank is probably water-logged (if it's a plain steel tank), or has lost it's air charge (if it's a bladder tank). This means that the water has nowhere to expand as it heats up when the boiler fires, so the relief burps out a little water. This also means that when the heating system cycles-off, the make-up water valve adds water back into the system as the pressure falls. Short term, this isn't a big deal, but long term, this constant addition of fresh water will result in oxygen corrosion of any ferrous components in your system.

 

[TheHub]

I agree with TBP this is a common occurance in both heating systems and in home water systems that include a well pump. If this were a water system the pump would short cycle due the quick reduction of pressure, no compressible bubble. The few drops from the relief could be the best clue. The relief is performing as a thermal relief and not like a safety or pressure relief, which are sized for much greater flow resulting from high temperatures and/or steam bubbles. It appears the system is water solid and that incompressible fluid is going through a small expansion with the temperature change. If your system has a plain steel tank, and you don't have a schrader valve to add air, let the tank drain if possible to restore the air bubble in the tank. If it has a good bladder restore air pressure to the bladder. DON'T GET BURNED with the hot water.

 

[imok2]

I agree with TSP and Thehub, the expansion tank has lost is's air charge.

 

[sznic]

OK,
I've drained the bump tank, seems to me like it was full, after that I filled it again, it reads about 5psi on the boiler gauge. I do not know what it should read, I can adjust water pressure regulator up or down, does it sound about right, 5psi that is?

 

[imok2]

You need to have an air cushen in the tank and maintain this pressure 5# at all times, that's why the expansion tank is called the (point of no pressure change). As the water heats up it will epand into the tank but as long as you have air in the tank it will keep a constant pressure on the system. If you lose the air then you have to find where the air is leaking out and fix it. Hope this helps.

 

[imok2]

PS the system pressure must always be lower then the relief valve setting so ck the system as it cycles off to make sure it doesn't go above the valve setting. if it does then you probably don't have enough air in the x-tank or to put it another way you have too much water in the x-tank. I know, it's very wordy!!

 

[sznic]

Thanks to all who replied and helped, I will keep you posted.

 

[sznic]

Just to let you know, draining bump tak and refiling it worked, pressure stays the same all the time, even with furnace on, pressure does'nt go up, thanks for great advise.