Water Leaking From Water Heater Drain Valve: The Fix

By Ray Bennett · Updated 2 October 2026 · 6 min read · General guidance, always check your own manual

Water Leaking From Water Heater Drain Valve: The Fix

Short answer

First work out which of two leaks you have. Water weeping out of the open end means grit under the seat, and opening the valve fully for a second usually clears it. Water at the joint where the valve screws into the tank means the valve has to come out. A three dollar brass cap stops the first one for good.

A leaking water heater drain valve is a cheap part and a short job, and one of the few tank faults that is genuinely small. The trick is telling which of two leaks you have, because they need different things.

One is grit sitting under the seat. The other is the joint where the valve screws into the tank, and that one is a bigger job.

Before you start

What to carry: a garden hose, a bucket, gloves and a pipe wrench if it comes to changing the valve. Ten minutes for the quick fixes, an hour if the valve has to come out.

Gas or electric? The valve is the same part on both. It only matters when the tank has to be drained, because a gas heater is turned off at the gas control on the front and an electric one at the breaker.

How hot is that water? It can come out of the bottom of the tank hot enough to scald, Rheem warns. Gloves on, hose pointed somewhere safe, and keep your face out of the way.

Make sure it really is the valve

A drip at the open end and a wet joint at the tank are two different faults. One is ten minutes, the other means the valve comes out.

Check 1

Dry everything, lay paper down, come back in an hour

Wipe the valve, the floor and the bottom of the tank completely dry. Put a sheet of paper or a piece of kitchen towel underneath and leave it.

Wet at the open end of the valve means the seat is not sealing. Wet where the valve meets the tank means the joint.

Wet paper further back, or water running down the outside of the tank from higher up, is neither. That is a different job, and the two usual candidates are the relief valve pipe above it or the tank itself: finding where a water heater is actually leaking.

One thing not to do, and one to do first. Never just tighten a plastic drain valve. They are moulded plastic, they have been cooked in hot water for years, and they crack. A drip you could have capped cheaply turns into a tank emptying itself across the floor.

Before the valve comes out, the tank has to be drained below it, which for a bottom valve means drained completely. Gas or power off, cold water valve on the top of the tank closed, a hot tap open upstairs, and the hose run somewhere that can take forty gallons of hot water.

The fixes, in the order to try them

Work down them. Step three is only needed for a leak at the tank joint.

Check 2

Open it fully for a second and blow the grit out

This is often a drip that started right after somebody drained or flushed the tank. A piece of grit comes down with the water, lodges under the seat, and the valve can no longer close on it.

Put the hose on, aim it somewhere safe, open the valve fully for a second or two so a proper rush of water goes through, then close it firmly by hand.

Do that two or three times. Once the grit is gone, the seal usually takes again. If the tank is full of grit to begin with, the same flush is worth doing properly: how to get the sediment out and keep it out.

Check 3

Screw a brass cap onto the open end

Every drain valve ends in a standard garden hose thread, and a brass cap with a rubber washer inside screws straight onto it. Plenty of heaters are sold with one fitted from new for exactly this reason.

Hand tight and then a nudge with a spanner is enough. The washer does the sealing.

That stops a weep at the seat permanently, and it costs less than a coffee. It does nothing at all for a leak at the tank joint, which is why the paper test above comes first.

Changing the valve

Check 4About an hour

Drain it, swap it for brass, refill it

Have the new valve in your hand before you start, because a plastic one often breaks as it comes out and then the tank cannot be closed again.

Gas or power off. Close the cold water valve on top of the tank, open a hot tap upstairs, put the hose on and drain it right down. Then unscrew the old valve with a pipe wrench.

Wrap the threads of the new one three or four times with plumber’s tape, in the direction it will screw in, and fit it snugly. Do not lean on it.

Buy a three quarter inch brass full port ball valve rather than another plastic one. It costs a little more, and its wider opening drains a tank faster.

Check the length before you buy. Some tanks have thick foam insulation around them, and a short valve will not reach through to the water. If yours sits deep, you need a nipple extension with it, which is another small part.

Then close the drain, open the cold inlet, and leave that hot tap running until the water comes out steadily with no spitting. Only when it is completely full does the gas or the breaker go back on.

Why it started after a flush

This is a common version of the whole problem, and it catches people who were doing the right thing.

Draining a tank drags years of grit across a seat that has not moved since the day it was fitted. Some of it stays there. The valve felt fine before because it had never been opened.

It is not a sign you damaged anything. Step one usually clears it, and the brass cap covers you if it does not.

The other pattern worth knowing is a valve that starts weeping and a tank that has also started rumbling. Both are the same grit, and the tank is telling you it is overdue: what each noise means.

Questions people ask

Is a cap really safe, with tank pressure behind it?

Yes, on a brass cap with the washer in it. That is the same pressure the valve body already holds, and manufacturers ship heaters with one fitted. A plastic cap or one without a washer is not the same thing.

Can I fit the new valve without draining the tank?

There are tricks for it and none of them are worth forty gallons of hot water across a basement floor. Drain it.

The drip only appears when the heater is running.

Then look above the valve first. A tank warming up pushes pressure through the system, and what that usually shows up is the relief valve: why a relief valve drips and what it is really telling you.

My valve has a screwdriver slot instead of a handle.

Same part, same fixes. Turn it with a flat screwdriver rather than a coin, and it still wants to be closed firmly rather than forced.

How long should the new one last?

A brass ball valve will outlive the tank. That is the main reason to spend a little more rather than fitting plastic again.

There is water under the heater but the valve is dry.

Then the leak is somewhere above and running down. Dry everything, paper on the floor, and work upwards from the valve to the pipes and then the tank itself.