Water Heater Pressure Relief Valve Leaking: 3 Causes

By Ray Bennett · Updated 2 October 2026 · 7 min read · Checked against the maker’s manual

Water Heater Pressure Relief Valve Leaking: 3 Causes

Short answer

A water heater pressure relief valve leaking is usually reporting a fault somewhere else. House pressure over 80 psi, water expanding with nowhere to go in a closed system, or water that is simply too hot. Only after those three is it the valve itself, and fitting a new valve without checking them gets you a new valve that drips the same way.

A water heater pressure relief valve leaking is usually reporting a fault somewhere else in the plumbing. The valve is doing its job. Something is pushing it open.

That is why replacing it first is the common mistake. A new valve on an unfixed system drips exactly the same way. Rheem says replacing the relief valve will not correct a thermal expansion problem.

Before you start

What to carry: a garden hose, a pipe wrench and a pressure gauge that screws onto a hose tap, which is cheap. Half an hour, and most of it is watching a needle.

Gas or electric? It changes nothing about this valve, which is the same part on both. It matters only if the cause turns out to be water that is too hot, because a gas heater is turned down at the dial on the front and an electric one at two thermostats behind the panels.

Is it really the valve? Follow the pipe. Water at the bottom of the discharge pipe means the valve opened. Water running down the outside of the tank, with a dry valve, is a different job: finding where a water heater is leaking.

How is it leaking? A slow weep that comes and goes points at pressure. A steady run means the valve is no longer sealing. A blast of hot water or steam means stop and read the box below.

Two things to get right before anything else. Never cap, plug or fit a valve into the discharge pipe. That pipe is the way out for a tank that is over pressure, and blocking it is how a water heater becomes an explosion rather than a leak. It also has to stay unthreaded at the bottom so nobody can screw anything onto it.

If the valve is discharging genuinely hot water or steam, or the tank is making a boiling noise, the water is running away with itself. Shut the gas off or the breaker, shut the cold water valve into the top of the tank, and get somebody out. That is the one version of this that is dangerous.

What the valve is actually for

One valve, two jobs. It opens if the pressure goes too high or if the water goes too hot, and the pipe takes the discharge safely to the floor.

It is called a temperature and pressure valve because it watches both. On a normal residential heater it opens at about 150 psi or about 210 degrees, whichever arrives first, and it closes again when the reading comes back down.

So a valve that drips is telling you one of three things: the pressure is too high, the water is too hot, or the valve has stopped sealing. The next three sections take them in that order, and Whirlpool’s own chart also puts a faulty valve last.

Read the pressure first

Check 1Five minutes

Screw the gauge on and read it cold

Put the gauge on an outside hose tap, or on the drain valve at the bottom of the heater, and open it with nothing running in the house.

Whirlpool says supply pressure should be around 50 to 60 psi and should not exceed 80. Over 80 is too high for a house, and a heater relief valve set at 150 is going to spend its life being nudged.

High static pressure is the street supply, and the answer is a pressure reducing valve on the main, or a new one if there is already an old valve that has given up. That is a plumber for an hour, not a new water heater.

Then read the temperature

Check 2

Run a hot tap into a cup and put a thermometer in it

Let a hot tap run for a minute so you are reading the tank and not the pipe.

Around 120 degrees is where a heater should sit. At 140 you are wasting fuel and risking scalds. Anywhere near 180 or 200 and the relief valve is opening because the water genuinely is too hot, and that is a thermostat problem rather than a plumbing one.

Turn the dial down and see whether the dripping stops. If the water keeps climbing with the dial turned down, the thermostat is stuck closed and is calling for heat that nobody asked for: how to test a water heater thermostat.

When the pressure only climbs while it heats

A closed system has nowhere to put the extra water, so every heating cycle pushes the pressure up until the valve lets it off.

This is the one most people never find, and Rheem and Whirlpool both name it as a cause of a valve that lets go now and then.

Leave the gauge on and watch it through a full heating cycle. If it sits at 60 cold and climbs to 120 or 150 while the burner or the element runs, you have thermal expansion in a closed system.

Rheem says water expands in volume as it heats. In an old house it simply pushes back into the street main and nobody notices. But if there is a check valve, a backflow preventer or a pressure reducing valve on your main, that route is shut, and the only way out is the relief valve.

Check 3

Fit an expansion tank, or check the one you have

An expansion tank is a small tank that hangs off the cold pipe near the heater with a rubber bladder and air behind it. The extra water squeezes the air instead of the relief valve.

If you already have one, test it. Take the cap off the little tyre valve on the end and press the pin. Air means the tank is doing its job. Water coming out means the bladder has split and the tank is now just a lump of pipe, which is why the dripping came back.

A working one should also feel light and hollow when you tap it. One that is full of water is dead.

When it is the valve itself

Check 4An hour

Pressure normal, temperature normal, still dripping

Then the valve is not sealing any more. Usually grit has got under the seat, often after somebody lifted the test lever on an older heater, and it will never fully close again.

To change it: gas off or breaker off, shut the cold water valve on top of the tank, open a hot tap upstairs, then drain a few gallons out of the bottom so the water level is below the valve.

Unscrew the discharge pipe, take the old valve out with a pipe wrench, wrap the threads of the new one, screw it in firmly, put the pipe back and refill. Watch it through a couple of cycles before you call it done.

While it is drained, if the tank also rumbles, it is worth flushing at the same time: what each noise means and how to flush it.

Questions people ask

Can I just put a bucket under it and leave it?

For a day while you get the parts, yes. As a way of living with it, no. The valve is wearing out while it does this, and the thing it protects you from is the one fault that does not give a second warning.

Should I test the lever every year like the label says?

Yes. Rheem and Whirlpool both say to lift and release the lever at least once a year. An older valve may not seal again afterwards, and Whirlpool says that if it keeps releasing water, turn the power off, close the cold water inlet and call a qualified person.

It only drips at night.

Typical thermal expansion. Nobody uses water at night, the heater still cycles, and the pressure has nowhere to go. An expansion tank stops it.

My expansion tank is only two years old.

Test it anyway with the tyre valve. They fail early when the air charge was never set to match the house pressure when it was fitted.

The discharge pipe is dry but there is water on the floor.

Then this is not your fault to fix here. Find where the water is actually coming from first, because a tank leaking from the bottom is a new heater rather than a repair.

How long should a relief valve last?

Rheem and Whirlpool give it no set life, only the yearly test of the lever. It is worth changing at the same time as any other work on the tank, since it costs almost nothing and it is already drained.

Sources: Rheem use and care manual AP23698 (thermal expansion, relief valve and discharge line, yearly lever test), Whirlpool Energy Smart use and care guide 318686-001 (supply pressure, closed system, drip from the T and P valve, discharge line) and the DOE Building America "Strategy Guideline: Proper Water Heater Selection" (2015) (relief valve settings of 150 psi and 210 degrees)