What the valve does
Every tank water heater has a temperature and pressure relief valve, usually on the top or upper side of the tank, with a pipe running down toward the floor or outside. It opens if pressure in the tank rises past its setting or if the water gets too hot. A steady drip, a gush every time the heater runs, or water at the end of the discharge pipe are all signs it is opening.
Sometimes the valve itself is the problem: mineral deposits from hard water or age can stop it from seating properly. But often the valve is working correctly and responding to real pressure or heat, which is why a plumber should test before replacing it.
Possible causes
| Cause | What happens | Usual fix |
|---|---|---|
| Thermal expansion on a closed system | Water expands as it heats and has nowhere to go, so pressure spikes | Add or replace an expansion tank |
| High street pressure | Incoming pressure is too high for the system | Install or adjust a pressure regulator |
| Failed pressure regulator | Regulator no longer holds pressure down | Replace the regulator |
| Thermostat or gas valve fault | Water overheats past the safe range | Repair or replace the control; often a serious fault |
| Worn or scaled valve | Valve no longer seals even at normal pressure | Replace the relief valve |
What to do now
- Turn the heater off.Gas control knob to OFF, or switch off the breaker for an electric heater.
- Keep people away.The discharge can be scalding. Keep children and pets clear of the pipe outlet.
- Note the pattern.Does it drip constantly, only while the heater runs, or only at night? This helps the plumber.
- Do not test the lever.On an old valve, lifting the test lever can leave it stuck open or dripping.
- Call a licensed plumber.Ask them to test water pressure and the thermostat before they swap the valve.
What a good discharge line looks like
Questions to ask
- What was the water pressure when you tested it?
- Is my water system closed, and do I need an expansion tank?
- Is the thermostat or gas valve holding the right temperature?
- Does the discharge line meet code where it ends?
Common questions
Can I replace the relief valve myself?
Swapping a valve without finding why it opened can hide a pressure or overheating problem. Have a licensed plumber test the system first.
Why does the valve drip only at night?
Street pressure often rises when demand drops overnight, and a closed system with no expansion tank can push the valve open. A pressure test can confirm it.
Is a dripping relief valve an emergency?
A slow drip is a warning; steam or a strong flow of hot water is urgent. Turn the heater off and call a licensed plumber either way.
General information for Brea, not a quote or professional advice. In an emergency, call 911.