Temperature and pressure relief valve discharging

Water expands as it heats, and on a closed system, where a backflow preventer or pressure-reducing valve stops the expanded water returning to the supply, the pressure climbs every time the tank fires. The relief valve is the pressure's release point: it lifts, drips into the discharge pipe, and reseats, over and over, which is the classic drip-during-heating pattern. The engineered fix is an expansion tank sized to the system, which absorbs the expanded water so the valve stays seated.

The test is timing: a valve that discharges only while the burner or elements run, then stops, is seeing expansion. A valve that runs continuously, or drips when the tank is cold, is more likely failed open or seeing supply pressure above its rating.

The discharge pipe must run to an approved location, must not be capped, plugged or valved, and must not have its end submerged: the valve is the tank's last pressure relief, and blocking it turns the tank into a pressure vessel. BC's plumbing code and every manufacturer manual are unambiguous on this, and the annual maintenance check exercises the valve so it does not seize.

A seized or weeping valve is a replacement part, and a valve that discharges because the tank is genuinely overheating needs the heating fault found, not the valve changed twice a year.

Discharge that has stained the floor or runs continuously is the moment to call: shut the cold supply if the discharge will not stop, turn the gas or power off if safe, and have the technician test supply pressure, the expansion system and the valve. Water damage restoration is separate from the heater work.