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RickInMissouri 01-23-2010 01:53 AM

Hydronic boiler pressure question.
I have a residential ďNationalĒ home water boiler with three zones, basement, first floor and second floor. Dual gauge on the boiler, the needles do fluctuate but Iím not sure if the pressure gauge is accurate. Old style expansion tank in the rafters near the boiler. I let too much air out of the expansion tank thinking this would resolve a noisy water flow issue, causing the below problem.

Hereís the Problem:
Water is now barely making it to the second floor register. The other two zones are OK but noisy with air in the lines, Iíll bleed them later.

Iíve read that this could be caused by not enough pressure in the system to push the water to the second floor as it is the compressed air in the expansion tank that does a lot of the work pushing the water. The expansion tank is either empty or no more than half full with water during operation so it is not water logged.

The boiler pressure gauge only shows 2 PSI but goes up to 5 PSI sometimes. When the boiler is turned off for a couple of hours to cool the pressure goes down to about 1 PSI. Iíve read it should be around 12 PSI. I shut it off for a few hours because I was going to add water.

The valves for the inlet water are both open.
Iíve tried lifting the reducer valve handle straight up to allow full water pressure in but hear no flow of water and the pressure gauge does not budge.

Do these pressure gauges typically fail completely and show 0 PSI or can they show inaccurate numbers instead?

Iím thinking that the pressure gauge is OK though since it does fluctuate, and that the reducer valve is corroded closed not allowing water in to pressurize the system. Does that sound like a reasonable conclusion?

*** As a temporary fix can I add water to the boiler through the drain valve or through the valve by the expansion tank, after it cools down first?

Iíll replace the reducer valve as a summer project if I can get around it for now.
Is the reducer valve serviceable? Can it be torn down, cleaned and reassembled?

Thanks for your time,


beenthere 01-23-2010 04:57 AM

Just replace it. Its not really servicable.

After refilling boiler, and bleeding rads.
Drain the expansion tank completely. If you don't when the boiler water heats back up, it will be full and the relief valve will pop open.

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