Illustration of a temperature-and-pressure relief valve with a drop of water at the discharge outlet.

Water Heater T&P Relief Valve Dripping

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The temperature and pressure (T&P) relief valve is a safety device that opens automatically if tank pressure or temperature gets dangerously high. A little discharge after it’s done its job can be normal; a valve that drips continuously or won’t fully close needs replacement — never cap, plug, or disable it.

Illustration of a temperature-and-pressure relief valve with a drop of water at the discharge outlet.
Illustration of a temperature-and-pressure relief valve with a drop of water at the discharge outlet.

Likely Causes, Ranked

  1. Excess system pressure
    Often from a failed expansion tank or a water pressure regulator issue on the home’s supply.
  2. Thermostat set too high or malfunctioning
    Pushes tank temperature into the valve’s trigger range.
  3. Worn or failed valve
    Valves don’t last forever — a valve that won’t reseal after opening once needs replacing regardless of cause.

Step-by-Step Diagnosis

  1. DIY WITH CAUTION
    Test the valve by lifting its lever briefly (if accessible and you’re comfortable doing so)

    Water should flow, then stop cleanly when released. If it doesn’t fully stop, the valve needs replacement.
  2. DIY WITH CAUTION
    Check if you have an expansion tank and whether it’s still working

    A failed expansion tank is a common cause of repeated pressure-relief drips.
  3. DIY WITH CAUTION
    Check your home’s incoming water pressure

    Over 80 psi is generally considered too high and stresses the whole system, not just the water heater.
  4. PRO ONLY
    Never cap, plug, or remove the discharge line

    This valve exists to prevent a genuinely dangerous pressure buildup — disabling it is not a safe workaround under any circumstance.
  5. PRO ONLY
    If the valve won’t stop dripping after testing

    Replace it — this is a straightforward job for a plumber and not one to defer for long.

FAQ

Can I just plug the pipe from a dripping T&P valve?

No — never. This valve exists specifically to prevent a tank from becoming a pressure hazard. If it’s dripping too much, replace the valve or fix the underlying pressure/temperature cause, don’t block its outlet.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

  • Standard T&P valve safety function, consistent across all major manufacturers’ documentation

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