A leaking temperature and pressure relief valve means one of two things: the valve itself has failed, or the system is genuinely over-pressurized or overheating and the valve is doing exactly what it was designed to do. The second possibility is why you should never simply cap or plug it.
What the T&P Valve Does
It is the water heater’s primary safety device. If tank temperature or pressure exceeds safe limits, it opens and releases water to relieve that pressure. Without it, an overheating tank becomes a genuine explosion hazard. That is why plugging a dripping T&P valve — which people do — is one of the most dangerous shortcuts in home plumbing.
Why It Might Be Discharging
- Excess water pressure. High incoming municipal pressure, or a failed pressure reducing valve. This also damages fixtures and supply lines throughout the house.
- Thermal expansion in a closed system. When a backflow preventer or check valve stops water from flowing back into the main, heated water has nowhere to expand. An expansion tank solves this, and its absence is a very common cause.
- A failed or waterlogged expansion tank. They do fail, and when they do the symptom is a weeping T&P valve.
- Overheating. A failed thermostat or gas control letting tank temperature climb too high. This is the serious case.
- A worn valve. Mineral buildup on the seat prevents a clean seal — common in Albuquerque’s hard water. Once a valve has weeped, it often will not reseat.
What a Plumber Will Actually Check
Incoming water pressure at a hose bib, the presence and condition of a pressure reducing valve, whether the system is closed and has a properly charged expansion tank, actual water temperature at the tap versus the thermostat setting, and the valve itself. Replacing the valve without finding the cause means it will discharge again.
Do Not Do These
Do not cap, plug, or tighten the valve closed. Do not remove the discharge pipe — it exists to direct scalding water safely toward the floor or a drain rather than at someone standing nearby.
Prevention
The T&P valve gets tested during annual water heater maintenance — it can seize shut with no outward sign, which is the failure nobody sees coming.
