Of all the drips a water heater can produce, the one from the temperature and pressure relief valve — the little brass valve on the side with the pipe running down — is the one that deserves your full attention. Not panic, but attention. That valve is the tank's safety release, and when it starts letting water out, it's either tired or trying to tell you something. Either way, ignoring it isn't a plan. Let's talk about what's actually going on.
What the T&P valve is for
Your water heater is a sealed steel tank holding very hot water under pressure. The T&P valve is designed to open around 210°F or 150 psi — venting water or steam through its discharge pipe — if temperature or pressure climbs too high. It's the reason a water heater is an appliance instead of a hazard. So when it drips, think of it less as a malfunction and more as a message. The question is what the message says.
Message one: the valve is simply worn out
Like any mechanical part living in heat for years, the valve's spring weakens and its seal hardens. A worn valve weeps or dribbles even when temperature and pressure are perfectly normal. This is the simpler outcome — the valve gets replaced with one correctly rated for your tank, the discharge pipe gets verified, and life goes on. We see this constantly on older units.
Message two: the pressure is genuinely too high
This is the more interesting case. If your plumbing is a closed system — common where there's a pressure-reducing valve or check valve on the main — heated water has nowhere to expand, so pressure climbs with every heating cycle. A failed expansion tank (that small tank hanging nearby) is the classic cause: its internal bladder gives out, the cushion of air disappears, and the T&P valve becomes the system's pressure relief by default. A thermostat letting water get too hot can do it too. In this case, replacing the valve alone won't help — the root cause needs fixing.
The one thing you must never do
Please don't cap the valve or plug the discharge pipe to stop the drip. We say this on nearly every T&P call because someone, somewhere, always suggests it. Capping removes the tank's protection against excessive pressure — it turns a warning into a hazard. If a previous homeowner capped yours, that's the first thing to correct, before anything else.
How we sort it out
Diagnosis is straightforward with the right tools: we measure your home's water pressure (around 40 to 60 psi is normal; sustained readings above 80 are high), check the expansion tank's air charge and bladder, and observe the system through a heating cycle. Then we fix what's actually wrong. If your T&P valve has become a regular dripper, call (833) 713-2101 — we'll read the message properly.