Why Is My Water Heater Relief Valve Leaking?
A water heater relief valve leaks for one of two reasons. Either the valve is worn and no longer seals, or it's doing its job and letting out pressure or heat that's too high. A constant drip usually means a worn valve. Water that comes out now and then usually means thermal expansion, which an expansion tank installation fixes. A worn valve calls for a relief valve replacement.
The temperature and pressure relief valve, or T&P valve, is the most important safety part on a tank water heater. It's the brass valve on the top or upper side of the tank with a lever and a pipe running down toward the floor. When it lets water out, that water usually lands at the bottom of the heater, so many people think the tank is leaking when it isn't.
Safety: Never cap, plug, or put a valve on the relief pipe to stop a drip. A blocked T&P valve takes away the one thing that keeps an overheated tank from bursting.
What Does a T&P Relief Valve Do?
The valve opens if either of two limits is reached: tank pressure gets too high (most residential valves are rated for 150 psi) or the water gets too hot (most open around 210°F). When it opens, hot water flows out through the discharge pipe instead of building up inside the tank. Once things are back to normal, the valve should close tightly again.
The pipe from the valve should be full size, run downhill, and end a few inches above the floor, the drain pan, or another approved spot where you can see it. It shouldn't be capped, threaded at the end, or reduced in size.
Steady Drip or On-and-Off? What Each One Means
Watch the end of the relief pipe for a day. The pattern tells you a lot.
| What you see | Most likely cause | Usual fix |
|---|---|---|
| Slow, steady drip all day | Worn valve seat or spring, often with mineral buildup | Replace the T&P valve |
| Water now and then, often after showers or on hot afternoons | Thermal expansion with no working expansion tank | Add or replace the expansion tank |
| Drips after you test the lever | Grit stuck in the seat after opening | Test again to flush it; replace if it keeps dripping |
| Hot water or steam pouring out | Tank overheating, possibly a failed thermostat or gas control | Turn off power or gas now and call |
| Water around the valve threads, not from the pipe | Leak where the valve screws into the tank | Reseal or replace the valve; check the tank |
Thermal Expansion: The Most Common Cause We See
Water expands when it heats up. In a 50-gallon tank, heating cold water adds a noticeable amount of volume. If your home has a pressure-reducing valve on the main line or a check valve at the meter, that extra water can't push back into the city supply. The pressure in your pipes climbs until the T&P valve opens to let it out.
Do I need an expansion tank?
If your plumbing is a closed system, usually yes. An expansion tank is a small tank with an air cushion inside, installed on the cold line near the heater. It soaks up the extra water as the tank heats, so pressure stays steady and the relief valve doesn't keep opening. Expansion tanks also wear out. When the air charge is gone, the valve starts dripping again.
Why does the valve drip more in summer?
In Apache Junction, cold-water lines can come into the house warm in summer, and heaters in garages and outdoor closets sit in very hot air. July highs average about 105°F. Higher temperatures all around mean more pressure swings, and a worn valve or tired expansion tank shows it first.
When the Valve Itself Is Worn Out
T&P valves don't last forever. With water at about 13–16 grains per gallon of hardness, minerals build up on the valve seat. Once that happens, the valve can't close fully and you get a constant drip. Rust on the spring can also keep it from seating.
Should I test my relief valve?
Many manufacturers suggest lifting the lever briefly about once a year to make sure water flows and the valve closes again. Be careful: the water is scalding. On an older valve that's never been tested, opening it can sometimes leave it dripping afterward. If that happens, the valve was likely due for replacement anyway.
Can I replace a T&P valve myself?
It's a common repair, but it means shutting off the water and heat, draining some water from the tank, and threading the new valve in properly. The replacement has to match the pressure and temperature rating on your heater's label. If you're not comfortable with any of that, we can handle it.
When a Leaking Relief Valve Is Serious
- Hot water or steam is pouring from the pipe
- Your hot water is much hotter than usual
- The tank makes loud rumbling or banging noises along with the discharge
- Water is coming from around the valve threads, which can point to tank corrosion
If any of these happen, turn off the gas or the breaker and the cold-water valve, and call us at (480) 555-0147. Our guide to shutting off a water heater shows where everything is.
If the relief valve checks out and the leak is lower down, see our water heater leaking from bottom page or the full leak finder. For pricing on valve repairs versus a new heater, see our water heater repair cost page. You can also go back to our Apache Junction leak repair homepage.
Relief Valve Leaking FAQs
Is it normal for a water heater relief valve to drip?
No. A relief valve should stay closed and dry unless pressure or temperature gets too high. Any regular dripping means either the valve is worn or something is pushing pressure up, most often thermal expansion without a working expansion tank.
Can I cap the relief valve pipe to stop the leak?
Never. Capping or plugging the relief valve or its pipe removes the tank's main safety protection. If pressure or temperature climbed with the valve blocked, the tank could burst. Fix the cause instead.
How much does it cost to fix a leaking relief valve?
Replacing a T&P valve is usually a service call plus the part, far less than a new water heater. If you also need an expansion tank, that adds the tank and labor. We'll explain the price before any work starts.
Why does my relief valve leak at night or after showers?
That timing usually points to thermal expansion. When the heater fires to reheat a tank of fresh cold water, the water expands. In a closed system with no working expansion tank, pressure spikes and the valve lets some water out.
How do I know if my expansion tank is bad?
Tap the tank. The top half should sound hollow and the bottom should sound full. If it sounds full all the way up, or water comes out of the air valve on the end, the internal bladder has likely failed and the tank needs replacing.
Can a leaking relief valve mean the tank is about to fail?
Not usually on its own. But water around the valve's threads, rather than from its pipe, can point to corrosion in the tank wall. If the heater is older and rusty around that spot, replacement may make more sense than a new valve.