Hot Water Boiler Overflow

Old 03-06-02, 05:11 AM
Visiting Guest
Posts: n/a
Hot Water Boiler Overflow

I have a 1983 HB Smith boiler with 2 zones. I recently noticed the pressure relief valve was discharging. The average pressure runs about 20-25 lbs. When the boiler fires up, the pressure rises to about 50 lbs, the boiler makes some minor popping noises and then discharges water. The pressure then drops to normal and then I hear the normal operation. There has to be some part that needs adjusting or replacing that I can do to save me a $500-1000 plumbers bill. Any suggestions? Thanks
Old 03-06-02, 05:52 AM
Visiting Guest
Posts: n/a
You did not say if the 20-25 PSI numbers were for a cold boiler or a hot boiler.

1) If the 20-25 PSI number you are refering to are when the boiler is cold, then it is too high. A cold boiler for a typical two story house should have an altimeter reading of 12-12 PSI.

When the boiler is hot, it will rise to 15-25 PSI.
Pressure relief valves discharges at 30-35 PSI.

If this is your scenerio, then your pressure regulator needs to be adjusted (via the center bolt on the unit) or else replaced.

2) If the 20-25 PSI numbers you are refering to are when the boiler is hot, this is OK. But the pressure relief valve going off is not normal. In this case your expansion tank is full (waterlogged).

Two types of expansion tanks exist.

a) Older Compression type: This type is about 10-15 gallons and has a pipe from the boiler and a pipe going to a drain faucet.
This type should be drained at least once a year. To drain this type, close the valve between the boiler and the expansion tank. Open the drain valve until all the water in the tank is gone. Then close the drain valve and re-open the valve between the boiler and expansion tank. It should fill 1/2 way with water (if you have a gauge on the expansion tank).

b) Newer Diaphram type: This type is about 5 gallons in size and has a single pipe going to the boiler. To test this one, you need to turn-off the autofill valve to the boiler and drain the boiler until the alimeter reads 0 PSI. Then with an tire gauge measure the pressure in the diaphram tank. It should be about 12-15 PSI, if not refill it with a tire pump. Then close the boiler drain valve and reopen the auto fill valve. It is probably necessary to bleed your radiators, since opening the boiler drain valve introduces air in your system.

Good Luck !


Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: