Issue with new water heater

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Mayers

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Hello everyone,

I recently installed a new electric water heater. The pressure relief valve keeps popping off non stop within seconds of water starting to fill the tank. Please note there is no expansion tank installed and there is no pressure reducing valve installed on the plumbing system. Also no back flow device.

I checked the pressure coming into the house and it's averaging around 130 to 140 PSI. My understanding is this is high and a pressure reducing valve would fix this. Would this also be the reason the pressure relief valve on the water heater is popping or could it have shipped with a bad pressure relief valve?

Should I go with an expansion tank first or the pressure reducing valve?
 

Smooky

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Most T&P valves are designed to open at 150 psi. If it is opening at a pressure lower than that, it could be a faulty valve. The pressure is very high so I would recommend installing a pressure regulator and expansion tank.
 
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Dj2

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Quote: "Should I go with an expansion tank first or the pressure reducing valve?"

You want to stabilize and reduce your in house pressure to between 50 and 80 first.
 

Reach4

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Should I go with an expansion tank first or the pressure reducing valve?
The PRV goes first, and the thermal expansion tank goes farther in. The tank is often placed near the water heater.
 

Mayers

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Thank you very much for your replies. I'll go home depot in the morning and get the PRV and expansion tank. :)

BTW my understanding is most PRV have a built-in backflow device? Is this correct?
 

Jadnashua

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If a PRV has a bypass valve, it won't open until the home pressure exceeds the supply pressure, which, kind of defeats the purpose of a PRV to keep the pressure stable. Without an ET, the pressure will cycle high enough to either return via a bypass, if present and working, or get high enough to cause the safety T&P valve to open.

While you may not have installed a check valve or had a PRV, it is quite possible that the utility company may have installed one in the line to your house. This is done to help protect their supply in case some pollution might try to push back into their system. IOW, a bypass may not work, since many utility companies are installing check valves, or will be as they get around to upgrading things. You should not rely on a bypass in a PRV to do much of anything.
 
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