Water Heater Leaking From the Relief Valve Pipe: Causes and Fixes

The pipe running down the side of a tank water heater carries water from the temperature and pressure (T&P) relief valve. Water coming out of it is a message about what is happening inside the tank.

What the flow pattern tells you

What you see	Likely cause
A steady drip all the time	Worn valve seat or debris in the valve
Dripping after the heater runs	Thermal expansion; no or failed expansion tank
Drips at night when water use is low	High street pressure
Hot water gushing out	Overheating: shut the heater off and call a pro

If hot water or steam is pouring from the pipe, turn off the gas or power to the heater and keep clear. That can mean the heater is overheating.

How to narrow it down

Check your water pressure with a gauge on an outdoor faucet. Very high readings point to the pressure-reducing valve.
Tap the expansion tank if you have one. A tank that sounds full of water has failed.
Check that the water temperature is reasonable at a tap.
Lift the valve's test lever briefly and release it; a valve that keeps dripping afterward may need replacing.

The fixes

A new relief valve with the ratings listed on the heater's label; see our pressure relief valve replacement cost guide.
An expansion tank on closed systems; see our water heater expansion tank installation cost guide.
A new pressure-reducing valve if street pressure is too high.
Thermostat or gas control repair if the heater overheats.

Never plug, cap or remove the relief valve or its pipe to stop a leak.

Why pressure rises in a closed system

Many homes have a check valve, backflow preventer or pressure-reducing valve where water enters. It keeps water from flowing back to the city main. When the water heater heats a tank of water, the water expands, but it has nowhere to go, so pressure climbs until the relief valve opens. An expansion tank on the cold line gives that water a place to go.

Checking your pressure

Screw a pressure gauge onto an outdoor faucet or the water heater drain valve. Normal household pressure is commonly in the range of about 40 to 80 psi. A gauge with a maximum-reading needle left overnight shows whether pressure spikes when the heater runs.

Common questions

Is it normal for a water heater relief valve to drip?

No. Occasional drips point to pressure or expansion problems, and constant drips to a worn valve. Both should be fixed.

Can I put a cap on the relief valve pipe?

Never. The valve and its pipe must stay open so the tank can relieve dangerous pressure or temperature.

Water heater leaking from the relief valve pipe