Trouble shoot relief valve spitting water?

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bc canada
My grandmother just had her water service upgraded as the old one was leaking. Now has a 1” supply.

Since this, she has noticed that her electric hot water tank keeps spitting water from the relief valve.

There is no expansion tank.

From what I can tell (all visible pipe) there is no check valve on the new water main or PRV. I don’t believe the PRV is required as the city pressures are within code range.

The obvious solution is adding an expansion tank to the HWT. But in theory, this shouldn’t be required if there’s no check valve, correct? Is it possible that the upsized line, 1” from 1/2” has increased pressure such that we need an expansion tank anyway?

Is there something else that could be faulty and causing this issue?
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Jeff H Young

In the Trades
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No its not related to pipe size the pipe could be 10 inch or 1 inch. but debris from the work, sputtering of air , wide swings in pressure give the tandp a work out and some times they recover and sometimes they dont. Tand p valves go bad sometimes when they are new sometimes old Maybe someone else knows had a brand new waterheater do that not long ago It was about 10 houses away from my house I tried 3 times few days or hours later same thing all over again. I cant blame anyone . I replace them ill give it try working the lever on and off but eventually it might cost 15 bucks for a new one. I suppose a few grand for a water main Ill eat a Tand P but turn off water to change a hose bib Im not paying for T and p plus labor if I as a plumber didnt cause it


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1. It is likely that there is a check valve that you are not aware of.
2. Get a garden-hose-thread pressure gauge. Monitor the pressure after a hot shower, and then stop all water use. I suspect that the pressure will rise to about 150 psi.
3. If water spits out while the pressure is not near 150 psi, the T&P valve needs replacing.

It is likely #1 is the deal, and you need a big-enough thermal expansion tank.
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