- DIY difficulty
- Moderate
- Time
- About 1 hour
- Parts cost
- Valve + tape, typically under $50
- Pro price
- $225
Tools & materials
- Replacement T&P valve (match label rating)
- Pipe wrench (x2)
- Thread-seal tape or pipe dope
- Water pressure gauge (hose-bib type)
- Garden hose and bucket
What the temperature and pressure relief valve does
The T&P valve (also called a release valve or pressure valve) sits on the top or upper side of the tank, with a pipe running down toward the floor. It opens automatically if the tank’s pressure or temperature gets too high, usually above 150 psi or 210°F. It’s the most important safety device on a water heater.
Why water heater relief valves leak
| Cause | Clue | Fix |
|---|---|---|
| High house water pressure | Gauge reads above ~80 psi | Install or adjust a pressure-reducing valve (PRV) |
| Thermal expansion | Leaks after the heater runs, or the house has a PRV or check valve | Add a thermal expansion tank |
| Worn or corroded valve | Normal pressure, but the valve still drips | Replace the T&P valve |
| Overheating | Very hot water or steam from the pipe | Shut off the heat and call a pro, because the thermostat may have failed |
Test before you replace
- Check the pressure. Screw an inexpensive pressure gauge onto an outdoor hose bib or the heater’s drain valve. Above about 80 psi is high. Watch it while the heater runs too, since a climbing reading means thermal expansion.
- Test the valve. Put a bucket under the discharge pipe and lift the test lever for a few seconds. It should release a burst of water, then snap shut. If it keeps dripping or won’t open, replace it.
How to replace a water heater T&P valve
- Get the right valve. Match the pressure, temperature and BTU rating on your heater’s label. Most residential tanks use a 3/4" valve rated 150 psi / 210°F.
- Turn off the heat (gas to “Off” or “Pilot,” or the breaker off) and shut off the cold water supply.
- Relieve pressure and drain. Open a hot tap, then drain enough water through the drain valve to get below the T&P opening. If it’s on the side of the tank, that may be 5–10 gallons.
- Remove the discharge pipe, then unscrew the old valve counter-clockwise with a pipe wrench.
- Install the new valve. Seal the threads, thread it in by hand, then tighten so the outlet points down.
- Reconnect the discharge pipe. It must be the same size as the valve outlet, run downhill, and end about 6" above the floor or at an approved drain. Never thread or cap the end.
- Refill, bleed the air, and check for leaks. Then restore the heat.
When to call a pro
- Your house pressure is high, so you need a PRV or expansion tank. That’s plumbing work and often needs a permit.
- The valve is seized or the threads are badly corroded.
- There are any signs of overheating.
A fair price for a pro T&P valve replacement is about $225, including a pressure test. An expansion tank is listed with the other add-ons on our water heater replacement page.
Frequently asked questions
Why is my water heater pressure relief valve leaking?
The three usual causes are high water pressure in the house (over about 80 psi), thermal expansion in a closed system without an expansion tank, or a worn valve that no longer seals. Find the cause before you replace the valve, or the new one will leak too.
Is a leaking T&P valve dangerous?
A small drip is usually a pressure or valve-wear problem. But if the valve is discharging very hot water or steam, the heater may be overheating. Turn off the gas or power immediately and call a pro.
Can I plug or cap a leaking relief valve?
Never. The T&P valve is the safety device that stops a tank from bursting if the thermostat fails. Capping it, or the discharge pipe, is extremely dangerous.
How often should a T&P valve be replaced?
Many manufacturers suggest testing it once a year and inspecting it every few years. Replace it if it leaks, won’t reseat after testing, or shows corrosion. Many pros replace it whenever they service an older heater.
What rating should a replacement T&P valve have?
Match the rating on your heater’s label. For most residential tanks that’s a valve rated 150 psi / 210°F, with a BTU rating at or above the heater’s input.