Hot Water Heater – Pressure Relief Valve

[Donnie King]

I am experiencing problems with a 4-year old GE natural gas hot water heater. Whenever the unit fires up, the pressure relief valve opens and hot water comes out at a steady rate. Once the heating cycle is completed, the pressure relief valve soon reseats and the flow of water stops. I am on city water and have been advised by the city that my water pressure is between 60 – 70 psi. The manufacturer states that the PRV will begin to open at 125 – 130 psi and will fully open at 150. The unit’s thermostat is set well below the “normal point” (actually closer to the vacation setting). Until recently, the unit has operated without incident over the past four years. There have not been any nearby changes with the city’s water distribution system and none of my neighbours are experiencing any problems with their systems. My system does not have a thermal expansion tank.

[CincinnatiPlumbingParticipant]

If you have a pressure reducing valve without a built in bypass, you need an expansion tank (some codes require them even if the PRV has a bypass). Check to see if you do have a PRV even though the city states the water main pressure to be within acceptable limits…you still might have one. If so, install an expansion tank.

Debris may have gotten into the T&P valve body and isnt allowing it to seat properly. However, I’m more inclined to think the T&P is just worn out as it is only happening during the heating cycle and not at all times. Replacing the T&P is a pretty straight forward process. Turn off the water to the heater, drain the tank down to a point that the water level is below the T&P, unscrew the old one, apply teflon tape and pipe dope to the new one, screw it in, turn the water to the heater back on.

Good luck

[Retired plbg1Participant]

Do you have expansion tank on the WH, if you do it might be water lodged. If sometimes heats up fast and builds a pressure no where to go so it goes out RV thats what it is made for, if you keep getting problems and dont have a Ex. Tank on WH have one installed and put on new RV.

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Art retired plbg

[SelgasParticipant]

I note you say you do not have an expansion tank fitted – that being the case the water contained within the gas cylinder is heated by the burner and expands, in doing so the pressure and temperature relief valve operates to protect the entire system. Once it opens it discharges hot water to waste. Over time these valves become less acurate and begin to fail – down here we recommend that the TPR valves be replaced at intervals not less than 4 years for this very reason. Sounds to me like a simple replacement valve will put things back to where you were originally. If your Plumbing code allows the non use of an expansion tank you could fit a cold water relief valve to the inlet cold water pipe just before the cylinder which should be set at 70% of the ppressure the hot water valve is set for. This will make the expansion take place on the cold water inlet line and push mainly cooler water to waste thus saving you costs in wasted energy.

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Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians

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