The temperature and pressure relief valve (T&P valve) on your water heater is a safety device. If pressure or temperature inside the tank gets too high, it opens and releases water. A dripping relief valve is telling you something.
Never cap or plug it
Capping a relief valve removes the tank's last line of defense against too much pressure. Don't do it, and don't let anyone else do it.
4 common causes
1. No expansion tank, or a failed one
In homes with a pressure reducing valve or check valve, heated water has nowhere to expand without an expansion tank. Pressure builds every heating cycle and the relief valve lets some out.
2. High house water pressure
If the pressure reducing valve has failed, pressure can exceed the safe limit and push the relief valve open.
3. A worn-out relief valve
Relief valves can wear out or get debris on the seat and drip even at normal pressure.
4. Water temperature set too high
Very high temperature settings can make the valve open.
What to do
- Make sure the discharge line is draining somewhere safe.
- Check your house water pressure with a hose-bib gauge. Over 80 psi is too high.
- Look for an expansion tank on the cold line above the water heater.
- Call a licensed plumber to find and fix the cause.