What the T&P Valve Does and Why It Matters
The temperature and pressure (T&P) relief valve is the single most important safety device on your water heater. Its job is to open and release water if the temperature climbs too high (typically above about 99°C / 210°F) or the pressure exceeds a safe limit (usually 150 psi). Without it, a malfunctioning tank could over-pressurize and rupture violently.
The valve connects to a discharge pipe that runs down toward the floor. So when the valve releases, you see water near the base of that pipe. A T&P valve that drips is doing one of two things: responding to a real over-pressure or over-temperature condition, or failing because its internal seat has worn out. Both need investigating — never plug or cap the discharge pipe to stop the drip.
Why Your T&P Valve Is Leaking
Excess pressure in the system. The most common real cause is high water pressure. Metro Vancouver municipal pressure can run high in some areas, and a closed plumbing system (with a check valve or pressure-reducing valve on the main) prevents expansion, so heated water has nowhere to go and the T&P valve weeps. The fix is usually a properly sized expansion tank.
Thermal expansion. Each time the burner heats the water, it expands. Without an expansion tank, that extra volume raises pressure and forces the T&P valve open near the end of each heating cycle.
Temperature set too high. A thermostat cranked past 60°C can push the valve toward its temperature trip point.
A worn or faulty valve. T&P valves age. Mineral buildup or a degraded seat can make them drip continuously even when pressure and temperature are normal. After a few years, the valve itself may simply need replacing.
How a Technician Diagnoses It
A proper diagnosis starts with measuring static water pressure at a hose bib and checking for thermal expansion. If pressure is high or climbing during heating cycles, the answer is an expansion tank and possibly a pressure-reducing valve — not just a new T&P valve.
The technician also verifies the thermostat setting and confirms the valve's rating matches the tank. Only after ruling out pressure and temperature causes is the valve itself replaced. Swapping the valve without fixing an underlying pressure problem just moves the drip to a new valve weeks later. This is exactly the kind of root-cause work CanroHeat does on tank water heaters.
There is also a simple test the homeowner can report on. Note whether the valve drips steadily around the clock, or only spikes shortly after a long hot shower or a dishwasher run. A drip that follows hot water use strongly suggests thermal expansion and points toward an expansion tank. A constant, all-hours weep more often means the valve seat itself has worn out. Either way, sharing that detail when you call helps the technician arrive with the right parts.
What You Should Do — and Never Do
Do place a bucket under the discharge pipe to catch drips and protect your floor while you arrange service. Do note whether the drip is constant or only happens after hot water use, which helps the technician.
Never cap, plug, or remove the discharge pipe to stop the leak. That defeats the safety device and turns a dripping valve into a potential tank rupture. Never assume a dripping T&P valve is harmless — it is a signal that pressure, temperature, or the valve needs attention.
Tank and tankless water heaters are serviced by our parent company CanroHeat. For a safe diagnosis and an exact quote on the expansion tank or valve replacement your system needs, call 604-359-1081.