Of all the drips a water heater can produce, the one from the temperature-pressure relief valve deserves the most respect — and the least delay. That valve is a safety device, and its drip is either a worn-out part asking for replacement or a faithful warning about dangerous pressure. Here's how to tell which, and the one thing you must never do about it.
Here's the maintenance-coach version: what each part does, the warning signs it sends, and the habit that keeps it healthy.
What the TPR valve does
The TP valve is the tank's final safety net. If temperature approaches about 210°F or pressure approaches about 150 psi, the valve opens and dumps water — releasing the danger before the tank itself becomes the danger. It's simple, mechanical, and utterly essential.
Under normal conditions it should sit there silently for years, doing nothing. Silence is its healthy state; any drip is a message. Learning to read that message is the whole subject of this article.
Worn valve vs. high pressure: telling them apart
A worn valve drips or weeps steadily at normal system pressure — the spring is tired, the seat is fouled, and it can't hold its seal anymore. It often starts after someone tests the lever and it won't quite reseat, or just from years of service.
A pressure-driven valve discharges in episodes, often after heating cycles, and the underlying cause is elsewhere: a failed expansion tank, a faulty thermostat running too hot, or house pressure that's too high. Same drip location, completely different fix — which is why diagnosis comes before replacement.
Expansion tank's role
If your T&P valve discharges after every heating cycle, look at the expansion tank first. Its job is absorbing the pressure spike of heated water; when its bladder fails, the spike hits the T&P valve instead, which dutifully opens. The valve isn't broken — it's doing its job against a broken system.
We see this misdiagnosed constantly: valve replaced, drip returns, frustration follows. The maintenance-coach rule is to check the expansion tank — tap test, pressure gauge — before condemning the valve. Fix the pressure, and the 'bad valve' often turns out to be fine.
Why capping the valve is dangerous
Never cap, plug, or restrict the T&P discharge pipe. Doing so removes the tank's only protection against runaway pressure and temperature — turning a warning drip into a potential tank rupture. It's also against code everywhere, for good reason.
We mention this because the temptation is real: the drip is annoying, the cap is easy, and the danger is invisible. Don't. If the drip bothers you, that's the valve doing its job of bothering you — answer it with a diagnosis, not a plug.
How a technician diagnoses the drip
We start with a pressure gauge on the system and the expansion tank's tap test — the two fastest answers. Then we check thermostat behavior and look at the valve itself: its age, whether it reseats after testing, and whether the drip is steady or episodic.
The pattern tells the story. Steady weep at normal pressure: worn valve. Episodic discharge with pressure spikes: system problem. Both at once: both get fixed. Either way, you get the true cause explained before any part is replaced.
Replacement: what's involved
When the valve itself is the problem, replacement is straightforward: water and fuel off, the old valve unthreaded, a new valve of the correct temperature and pressure rating threaded in with proper sealant, and the discharge pipe routed correctly — full-size, downward, terminating where scalding discharge can't hurt anyone.
Then verification: the system is brought back up, the new valve is tested, and pressure is confirmed normal. And before we leave, you learn the annual test-lever habit, so this safety device never goes quiet on you.
Your maintenance takeaway
A dripping T&P valve is never 'just a drip' — it's a message about the valve or your system's pressure, and it deserves an answer. Read it, don't cap it, and build the yearly test into your routine. If yours is dripping now, call (833) 713-2101.