minor leak at hot water tank T&P valve

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qmqmqm

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Hi everyone.

Here is what happened at a townhouse:
A T&P valve leaks on an older hot water tank.
Replaced it with a new tank. Still leaks.
Changed the T&P valve on the new tank. Still leaks.
The leak is very slow - about a litre per week.
Turned down the valve a bit at the tank's cold water supply. It leaks less.

I'm not certain if the leak is constant or only happens sometimes.

City water pressure is normal. The tank is not over-heated. There is no pressure regulating device at the house.

What could be the problem, and the recommended solution?

Thanks!

Paul
 
How did you verify that your city water pressure is normal? Many times, the Pressure Reducing Valve will go out and will push 100PSI or greater down to your water heater, causing the T&P to fail. Also, I've been taught to never flip the valve open since it will push crud from the water heater and stop the seal from sealing. Go spend $13 and get a hose bib tester and verify your water pressure.

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By the way, we have dozens of professional plumbers at our sister site called:

www.plumbingforums.com

who are there to answer any technical plumbing issues you may have.
 
Did you happen to install the necessary expansion tank when you replaced the hot water tank?
Seems like this would solve your problem.
 
Thanks for your responses!

Havasu, a technician measured the water pressure to be 50 psi. This matches the Pressure Reducing Valve (PRV) on the main line. The PRV's label also reads "50 psi".
 
The Hot Water Tank's manual says if there is a Check Valve at its cold water supply, an expansion tank is required.

I have this valve at the cold water supply. Is it a check valve? Does the arrow mean it is a check valve?

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