Water heater relief valve leaking or dripping: what it means

What the valve does

The T&P valve opens to let water out if the tank gets too hot or the pressure gets too high. Watts, a major valve maker, says these valves open when the water in the heater reaches 210°F, or at the valve's pressure set point, typically 150 psi. A. O. Smith warns that if the valve doesn't work, the tank can over-pressurize and explode.

Dripping now and then

A. O. Smith's technical bulletin says intermittent weeping or dribbling means the valve is relieving pressure. In a closed system, pressure climbs as water heats. That's thermal expansion, and Watts says it's the typical cause of dripping.

Many homes have a check valve or pressure-reducing valve at the meter that keeps expanding water from flowing back to the street. With nowhere to go, the pressure builds until the relief valve lets some out. A thermal expansion tank gives that water somewhere to go.

A big gush of hot water

A sudden discharge of very hot water means the valve opened on temperature, A. O. Smith says. That points to a thermostat or gas control problem. Turn off the heater and call.

Leaking at the threads

Water seeping around where the valve screws into the tank is a connection leak. The valve needs to be removed and resealed. Rust or corrosion at that fitting can also be an early sign the tank itself is going.

Check your water pressure

The International Plumbing Code calls for a pressure-reducing valve where static water pressure in a building exceeds 80 psi. An inexpensive pressure gauge on a hose spigot tells you yours. Some systems run high: Post Falls, Idaho, for example, reports 65 to 75 psi on average, higher in the south of town (see our Post Falls page).

A. O. Smith advises controlling water pressure and installing a thermal expansion tank before replacing a dripping relief valve. Otherwise a new valve will just drip too.

What not to do

• Never cap, plug or remove the relief valve or its discharge pipe.
• Don't ignore it. Watts notes that a valve left dripping can build up minerals and eventually block, which defeats its purpose.
• Don't test it if it's old and you've never opened it. It may not reseal. A. O. Smith says to inspect it once a year, and have a professional look every five years.

Local pages mentioned

• Star, ID
• Post Falls, ID