Why Is My Water Heater Pressure Relief Valve Leaking?
A leaking T&P relief valve is often doing its job — releasing dangerous excess pressure. Here's what causes it and why you should never cap or ignore 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 is the relief valve 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.
A weeping relief valve is your water heater asking for attention. If water is showing up elsewhere on the unit, see why water heaters leak, 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.
Frequently asked questions
- Can I just replace a leaking relief valve myself?
- Even if the valve itself is worn, the leak is often a symptom of a real pressure or temperature problem that will persist after a swap. It's best to have the cause diagnosed — water pressure, thermal expansion, and the thermostat all need checking — so you're not masking a genuine safety issue.
- Is a leaking T&P valve dangerous?
- The leak itself is actually the valve protecting you by releasing excess pressure or heat. The danger is ignoring it — or worse, capping or plugging the valve, which defeats the tank's key safety system. Have the underlying cause diagnosed and corrected promptly rather than silencing the symptom.
- Do I need an expansion tank on my water heater?
- If your home has a closed plumbing system — common when a pressure-reducing valve or check valve is installed — an expansion tank absorbs the pressure created as water heats, and adding one often stops repeated T&P valve weeping. A plumber can test your system and confirm whether yours needs one.