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Posted by Dave on March 27, 2004 at 12:21:01:
On our Weil-McLain indirect water heater, the temperature setting is at 130. Our house has a booster pump/pressure tank which cuts-in at 50 and shuts off at 70. The only backflow preventer/check valve is before the water main enters the booster pump.
We also do not have an expansion tank at the water heater.
Last week I had installed a recirculating pump (autocirc is the brand name). The pump sits under the vanity in the master bath and takes water from the hot water line and circulates it back through the cold water line so there is always instant hot water.
The day after I put in the pump, the T&P valve discharged twice.
I found that the plumber had put the wrong T&P valve (100,000btu/hr vs the 200,000 btu/hr specified). Also, the temperature sensing bulb was too short so it was only in the pipe (not in the water in the tank).
I replaced the valve with the correct one and also put a pressure gauge on the hot water line at our washing machine (on the 2nd floor).
The pressure gauge has a "lazy hand" which will give the maximum pressure experienced by the system.
The autocirc pump has been running since yesterday, and the maximum pressure has been 75 psi. Also, the maximum temp I have seen at the water heater has been 140. The T&P is set to discharge at 150 psi or 210 degrees.
Can I assume that it was probably a bad T&P valve or could there still be an issue with pressure or temperature surges that I just haven't seen yet? In other words, how long should I watch the pressure in the hot water line before I decide the problem is fixed?