Water Heater Pressure Relief Valve Maintenance

Why the T&P Valve Matters

The temperature and pressure (T&P) relief valve is a critical safety device that prevents your water heater from becoming a dangerous pressure vessel. If the thermostat fails and water overheats, pressure builds inside the sealed tank. Without a functioning T&P valve, this pressure could cause a catastrophic tank explosion. The T&P valve opens automatically when water temperature exceeds 210°F or pressure exceeds 150 psi, releasing water through a discharge pipe to relieve the dangerous condition.

Annual Testing Procedure

Test the T&P valve at least once a year. Place a bucket under the discharge pipe end (which should terminate 6 inches above the floor or drain). Lift the lever on the T&P valve quickly and let it snap back. Hot water should discharge through the pipe while the lever is lifted and stop completely when released. If water continues to drip after releasing the lever, the valve seat is worn and the valve needs replacement. If no water comes out when you lift the lever, the valve is stuck and should be replaced immediately.

Replacing the T&P Valve

Turn off the water heater and close the cold water inlet. Drain the tank below the T&P valve level (usually a few gallons). Use a pipe wrench to unscrew the old valve from the tank. Apply Teflon tape to the threads of the new valve and thread it into the opening, tightening with a wrench until the overflow opening points downward. Reconnect the discharge pipe — it must run downhill to an appropriate drain point, without reductions in size, without traps, and without being plugged or capped.

Discharge Pipe Requirements

The T&P valve discharge pipe is subject to building code requirements for safety. It must be the same diameter as the valve outlet (usually 3/4 inch), made of approved material (copper or CPVC), and terminate where discharged water is visible but will not cause injury or property damage — typically 6 inches above a floor drain. Never plug, cap, or reduce the size of the discharge pipe. Do not connect it to a closed drainage system without an air gap. If you find the valve frequently discharging, do not simply replace it — the underlying cause (excessive pressure or thermostat failure) must be diagnosed and corrected.