What the valve does
Every tank water heater has a temperature and pressure relief valve, usually on the top or upper side, with a pipe running down toward the floor or outside. If the water inside gets too hot or the pressure climbs too high, the valve opens and releases water to bring it back down.
A valve that drips or discharges is either doing exactly that job, or it has worn out and no longer seals. Both are worth a professional look, because the first means something upstream is wrong and the second means your safety device is unreliable.
Common reasons it drips
| Cause | Clue | Usual direction |
|---|---|---|
| Thermal expansion in a closed system | Drips after the heater runs, stops later | Plumber checks whether an expansion tank or adjustment is needed |
| High incoming water pressure | Drips often; other fixtures also seem forceful | Pressure checked at a hose bib; regulator may need attention |
| Temperature set too high or thermostat fault | Very hot water at taps, steady discharge | Thermostat or gas control checked |
| Worn valve seat or debris | Steady drip regardless of use | Valve replaced by a plumber |
| Sediment interfering with the valve | Older tank, hard water, gritty discharge | Valve and tank condition assessed together |
What to do now
- Keep the area clear.Move anything stored below the discharge pipe and keep children and pets away from the outlet.
- Check the temperature setting.If the dial is set very high, note it. Very hot water both raises scald risk and can trigger the valve.
- Watch the pattern.Note whether it drips only after heavy hot water use, all the time, or only at night. That pattern helps the diagnosis.
- Call a licensed plumber.Ask for the valve, water pressure and thermal expansion to be checked together rather than just swapping the valve.
Words that come up
- T&P valve
- Temperature and pressure relief valve, the safety valve on a tank heater.
- Thermal expansion
- Water grows in volume as it heats. In a closed system it has nowhere to go, so pressure rises.
- Expansion tank
- A small tank on the cold line with an air cushion that absorbs expansion. Whether one is required for your home is a question for the city.
- Pressure regulator
- A valve where the water service enters the house that limits incoming pressure.
Questions for the plumber
- What is the incoming water pressure at my house?
- Is thermal expansion the cause, and what would fix it?
- Is the valve itself worn, and should it be replaced?
- Is the discharge pipe routed correctly for safety?
Common questions
- Can I just replace the relief valve myself?
- It is a safety device on a pressurized tank of hot water. Have a licensed plumber replace it and find out why it was releasing.
- Why does it only drip at night?
- Water pressure from the supply can rise when demand drops overnight, and the heater may also cycle then. Mention the timing to your plumber.
- Does a dripping valve mean the tank is failing?
- Not necessarily. It often points to pressure, temperature or expansion. But on an old, sediment-heavy tank, it is worth judging the whole heater.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.