Why Is My Water Heater Pressure Relief Valve Leaking?
A leaking T&P (temperature & pressure) relief valve is often doing its job — releasing dangerous excess pressure. Here's what causes it and why you should never ignore or cap it.
When your water heater’s temperature-and-pressure (T&P) relief valve is leaking, it’s usually doing exactly what it’s designed to do: releasing excess pressure or temperature to keep the tank from becoming dangerous. That makes a leaking T&P valve something you should never ignore, cap, or plug.
What the T&P valve does
The T&P valve is a critical safety device. If the water inside your tank gets too hot or the pressure climbs too high, the valve opens and discharges water to relieve it. Without a working relief valve, extreme pressure could, in the worst case, rupture the tank.
Why it’s leaking
Excessive pressure. If household water pressure is too high, or a closed system has no expansion tank to absorb thermal expansion, pressure builds until the valve releases it. This is one of the most common causes.
Excessive temperature. A thermostat set too high or a malfunctioning thermostat can overheat the water, triggering the valve.
Thermal expansion. As water heats, it expands. In a “closed” plumbing system (common with a pressure-reducing valve or check valve), that expansion has nowhere to go without an expansion tank, so pressure spikes and the valve weeps.
A faulty or worn valve. Sometimes the valve itself is failing — debris under the seat or simple age can cause it to drip even when pressure is normal.
What to do
First, understand that the valve leaking may be a symptom of a real pressure or temperature problem — not just a bad valve. The right fix depends on the cause: lowering the thermostat, adding or repairing a thermal expansion tank, addressing high incoming water pressure, or replacing a worn valve. Never cap or block the valve to stop the leak — that removes the tank’s key safety protection.
When to call a professional
A leaking T&P valve should be diagnosed promptly. A plumber can test your water pressure, check for proper thermal expansion control, verify the thermostat, and determine whether the valve or the underlying conditions need correcting.
Frequently asked questions
Can I just replace the valve myself? Even if the valve is faulty, the leak is often a sign of a pressure or temperature issue that will persist. It’s best to have the cause diagnosed so you’re not masking a safety problem.
Is a leaking T&P valve dangerous? The leak itself is the valve protecting you. The danger is ignoring it or, worse, capping it — which defeats the safety system. Have the cause addressed quickly.
Do I need an expansion tank? If you have a closed plumbing system, an expansion tank absorbs the pressure from thermal expansion and often resolves repeated T&P weeping. A plumber can confirm whether yours needs one.
A weeping relief valve is your water heater asking for attention. Learn more about our water heater service, or contact us any time — we’re available 24/7.
General guidance only. Never cap a relief valve; have a licensed plumber diagnose the cause.