The temperature-and-pressure relief valve is the last line of defense between normal operation and a dangerous overpressure event. When it drips, it’s telling you something — here’s how to listen.
What the T&P valve does
It’s a spring-loaded safety valve set to open around 150 PSI or 210°F — conditions that should never occur in normal operation. The discharge pipe runs down the tank’s side to safely direct vented water toward the floor. When you see that pipe dripping, the valve has either worn out or it’s legitimately venting excess pressure or temperature.
Cause #1: A worn-out valve (most common)
Years of heat cycles and mineral exposure degrade the valve seat until it can’t seal. The fix is a straightforward replacement — $150–$300, usually under an hour — with a correctly rated new valve.
Cause #2: Excessive water pressure
Household pressure above 80 PSI — common in foothill zones and homes without regulation — forces even a good valve to weep, especially during heating cycles. Replacing the valve without fixing pressure just buys another dripping valve. We measure pressure on every T&P call.
Cause #3: Failed expansion tank
On closed plumbing systems, heated water needs somewhere to expand. A waterlogged or failed expansion tank turns every heating cycle into a pressure spike — and the T&P valve takes the beating. The real fix is a new expansion tank ($200–$400), not a third new valve.
Cause #4: Overheating
A thermostat stuck on can drive tank temperature toward the valve’s 210°F trip point. Scalding-hot tap water plus a discharging valve is an urgent combination — call (833) 713-2101 promptly.
The one thing you must never do
Never cap, plug, or restrict the discharge pipe. It’s the tank’s emergency vent; blocking it removes the last protection against overpressure failure. It’s also a code violation. A dripping valve is annoying — a blocked one is dangerous.
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How much does T&P valve replacement cost?
$150–$300 in the Diamond Bar area, including diagnosis. If an expansion tank is the root cause, budget $200–$400 for that instead — or both.
Can I replace the T&P valve myself?
It involves draining the tank below valve level, correct valve rating selection, and proper discharge piping. Most homeowners are better served calling (833) 713-2101 — it’s a one-visit job.
Related Reading
7 Signs Your Water Heater Is Leaking (and What to Do Next) • What to Do When Your Water Heater Leaks: A Step-by-Step Safety Guide • Water Heater Leak vs. Condensation: How to Tell the Difference
Related service: Emergency Water Heater Leak Repair • Tank Water Heater Leak Repair • Tankless Water Heater Leak Repair