How often should I test the T&P relief valve?

Once or twice a year, most conveniently alongside the annual tank flush. Lift the lever, confirm a burst of water through the discharge pipe, let it snap back, confirm it stops.

Why does my relief valve keep dripping after I test it?

Debris caught on the seat, or a worn seat that testing dislodged into leaking. Cycle it once or twice to clear debris; a persistent drip means replace the valve, they are inexpensive and not repairable.

Is a discharging relief valve an emergency?

Steady discharge means the valve is doing its job against real overpressure or overtemperature. Treat it as urgent: verify the thermostat, check house pressure and thermal expansion, and do not cap or plug the valve under any circumstance.

What size and rating replacement valve do I need?

Match the original: residential tank valves are typically 3/4 inch, rated 150 psi and 210°F, with the rating stamped on the tag. The probe length must also suit the tank, so match the model rather than guessing.

Water Heater Pressure Relief Valve: Testing and Replacement

Page last reviewed: August 2026 · Reviewed by Harold R. Bennett, retired home inspector

The temperature and pressure relief valve is the one component on a water heater whose job is preventing a catastrophe rather than making hot water, and testing your water heater pressure relief valve takes thirty seconds a year. This guide covers what the valve protects against, the test, the meaning of drips and discharges, and replacement when the test fails.

What the T&P valve is for

A sealed tank of water with a heat source is, mechanically speaking, a boiler, and a boiler whose controls fail with no relief path can build pressure until the tank ruptures, violently. The T&P valve is the engineered escape: it opens automatically at 150 psi or 210°F, whichever arrives first, dumping water and pressure through a discharge pipe before the tank can approach failure. Every tank heater has one, threaded into the top or upper side, with a test lever and a discharge pipe that must run, unvalved and uncapped, down to within a few inches of the floor or to an approved drain.

That discharge pipe deserves respect in its own right: no cap, no plug, no threaded end that invites one, and no reduction in size, because a blocked discharge equals no relief valve at all. I have found them capped by owners tired of drips. That is disabling a safety device to silence its warning.

The 30-second annual test

Put a bucket under the discharge pipe outlet, or confirm it runs to a drain.
Lift the test lever fully for two or three seconds. Hot water should rush through the discharge pipe.
Release and let it snap closed. Flow should stop completely within moments.

Flow, then full stop: the valve passes. No flow when lifted means a frozen or blocked valve, and a valve that will not open is a failed safety device: replace it now. Flow that will not fully stop usually means debris on the seat; cycle the lever once or twice, and if the weep persists, the valve has told you its seat is done. The natural time for this test is during the annual flush, while you are already standing there with a bucket, and the same sediment the flush removes is a common culprit fouling valve seats.

Reading a valve that acts up on its own

Occasional small discharge, especially after heavy hot water use: classic thermal expansion. In homes with a closed system (a check valve or pressure-reducing valve at the meter), heated water has nowhere to expand, and pressure spikes lift the T&P briefly. The fix is a properly charged expansion tank, not a new relief valve, and this pattern is worth confirming with a gauge since chronic house pressure problems run in both directions.

Steady dripping: worn seat or debris, per above. Replace rather than tolerate, because a chronically weeping valve crusts over with mineral, and a mineral-crusted valve is on its way to being a frozen one.

Steady or repeated strong discharge: the valve is relieving a real condition. Check the thermostat setting, consider a stuck heating element or gas valve driving overtemperature, and verify house pressure. Until diagnosed, treat the heater with suspicion and, if discharge is continuous and hot, shut off the heat source and call it in.

Replacement

A failed T&P valve is a 15 to 30 dollar part and a homeowner-level job on most tanks. Kill the heat (breaker, or gas to pilot), close the cold inlet, open a hot tap, and drain a few gallons so the tank level sits below the valve port, the same setup as an anode inspection. Unscrew the discharge pipe, back the old valve out with a wrench, thread the new one in with PTFE tape so its discharge outlet aims correctly, reattach the pipe, refill, restore heat, and test once. Match the replacement’s pressure and temperature rating and probe length to the original, both stamped on its tag.

If the old valve will not budge, or the tank is old enough that disturbing fittings feels risky, that is a fair moment for a plumber, and possibly for the repair-or-replace conversation about the tank itself.

The bottom line

The T&P valve is the tank’s last line of defense, it gets tested with one lever-lift a year, and its three messages are simple: no flow means replace today, a persistent drip means replace soon or fix expansion, and a real discharge means find out why. It is the cheapest component on the heater and the only one that is not allowed to fail silently.