T&P Valve Leaking After Testing It: What It Means
On this page (5 sections)
The Short Answer: Lifting a relief valve’s test lever can loosen mineral deposits that then sit on the valve seat and stop it closing fully. A few drips for a short time afterward is common. A drip that continues for hours means the seat is fouled or worn and the valve usually needs replacing. Also have house pressure checked, since a test can reveal a valve that was already near its limit.
Normal settling or a problem?
| After the test | Likely meaning | What to do |
|---|---|---|
| A few drips, then dry within minutes | Valve reseated | Nothing further |
| A slow, steady drip from the discharge pipe that continues | Debris or scale on the seat, or a worn seat | Plan to replace the valve |
| Water flowing steadily and not slowing | Valve stuck open | See pressure relief valve stuck open |
| Lever will not return to its closed position | Stem or lever damaged | Replace the valve |
| Water around the valve’s threads, discharge pipe dry | Thread leak at the tank, not the seat | A fitting repair |
Why testing can start a leak
Relief valves on older heaters, especially in hard-water areas, may sit untouched for years while minerals build up around the seat. When the lever is lifted, hot water rushes past and loosens that buildup. Some of it can land on the seat as the valve closes, holding it open just enough to drip. A seat that was already pitted may also lose the mineral layer that had been sealing it.
Testing also reveals pressure problems. If house pressure is high, or the home has a closed plumbing system without a working expansion tank, the valve may have been close to opening anyway. A. O. Smith’s thermal-expansion bulletin (opens in a new tab) explains how that pressure builds. In that case, a new valve may drip too until the pressure problem is fixed. A brand-new heater that drips from its relief valve is covered in pressure relief valve leaking on a new water heater.
What you can check safely
- Watch the discharge pipe and note whether the drip is constant or happens mostly while the heater is heating.
- Make sure the discharge pipe runs freely to a drain or a safe location and is not capped, kinked, or blocked.
- Check the water temperature at a tap. Very hot water with a dripping relief valve suggests overheating; turn the heater off and call for service.
- Do not keep lifting the lever to try to clear it. Repeated operation can make a damaged seat worse or leave it stuck open.
What the plumber will check
A plumber will check house water pressure, the pressure-reducing valve if present, and the expansion tank’s charge before replacing the relief valve. The replacement must match the heater’s required temperature and pressure rating and BTU or kW capacity, as stated on the heater’s rating plate or in its manual, and the discharge pipe must meet local code. Replacing the valve is a routine repair; it does not mean the heater needs replacing.
Frequently Asked Questions
Q: How long is it normal for the valve to drip after testing? A: Usually only a few minutes. If it is still dripping after a few hours, the valve is unlikely to reseat on its own.
Q: Should I stop testing the relief valve? A: Manufacturers commonly recommend operating the valve periodically, as described in your owner’s manual, because a valve that is never exercised can seize. On an older valve that has not been operated for years, consider having a plumber test it so a replacement is on hand if it does not reseat.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith technical bulletin 45: thermal expansion (opens in a new tab)Background on pressure rise in a closed water system. Pressure testing and repairs are professional work.
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