The temperature-pressure relief valve — the T&P valve, the tank’s pressure whistle — sits on the side of the tank with one job: open near 210°F or 150 psi so the tank never has to contain more than it was built for. When it drips or discharges, it is telling one of two stories, and the fix depends entirely on which one.
Story one: the valve itself wore out — its spring weakened, its seat mineralized — and it weeps on its own. Story two: the valve is doing its job against genuinely excessive temperature or pressure, and the drip is an alarm. Here is how to read which story you have.
The TP valve's purpose
Think of the T&P valve as the tank’s pressure whistle and the discharge pipe as its voice. Under normal conditions it sits silent; when temperature or pressure climbs past what the tank should ever hold, it opens and vents water — loudly, visibly, safely. It is the last line of defense between a stressed tank and a ruptured one.
That is why one rule is absolute: never cap or plug a T&P discharge pipe. Capping it does not fix the pressure — it silences the alarm while the danger builds. The discharge pipe must run downward and terminate properly — the whistle needs its voice intact. A capped discharge turns a warning into a hazard.
Story one: the valve itself wore out
Springs weaken, seats crust with mineral, and seals harden — after years of heat cycling, a T&P valve can start weeping even when system conditions are perfectly normal. The signature: a constant, steady weep or drip that does not change with heating cycles, showers, or time of day.
The fix is a correctly rated replacement valve — matched to the tank’s BTU and pressure ratings, not a generic swap — with the discharge pipe properly terminated. We test-fire the new valve and verify it reseats before leaving.
Story two: the valve is telling the truth
If the valve discharges in bursts — especially after long heating cycles or heavy hot-water use — suspect real pressure or temperature events. The usual accomplices: a failed expansion tank bladder, an over-set thermostat, or house pressure running high. The valve is the messenger; shooting it fixes nothing.
This is where a gauge settles the argument. We measure system pressure and check it against what the valve is reporting — typical residential pressure runs 40 to 60 psi, and anything at 80 or above is high. Numbers, not guesses, separate the two stories.
The expansion tank link
In a closed plumbing system, every heat cycle expands the water, and with nowhere to go, pressure spikes. The expansion tank’s air bladder is the cushion that absorbs it — and when that bladder ruptures or waterlogs, the cushion is gone and the T&P valve discharges after every long heating cycle.
We test the bladder with a gauge and check its air charge against the home’s static pressure. A surprising share of “failed T&P valves” are actually failed expansion tanks wearing a valve’s disguise.
Reading the discharge pattern
Keep a simple log before you call: constant weep versus discharge after heating, versus discharge only after heavy use. A constant weep points at a worn seat; a gush after the burner runs points at pressure events; discharge timed to showers points at thermal expansion with a dead cushion.
Describe the pattern when you call (833) 713-2101 — it tells us which story the valve is telling before we arrive, and which tests to bring.
What a proper T&P visit includes
The full job: shut the water and heat source down, measure system pressure with a gauge, test the expansion tank’s bladder and air charge, install a correctly rated valve, terminate the discharge pipe properly, then test-fire the valve and restore service.
Done this way, both the valve and the reason are handled — so the new valve stays quiet instead of weeping again next month.
In short
A dripping T&P valve is either a worn part or a truthful alarm — and the discharge pipe stays open in both cases. Read the pattern, measure the pressure, fix the cause behind the symptom. Call (833) 713-2101 for water heater leak repair in Medford, MA that starts with the part, not a guess.