How to test a temperature and pressure relief valve

The temperature-and-pressure relief valve is the tank’s last mechanical safety device. It opens if the water gets too hot or the pressure gets too high, and it is supposed to close when conditions return to normal.

Testing it means lifting the lever briefly so a little hot water leaves through the discharge pipe, then confirming the valve shuts. That test can scald you, it can start a permanent drip if scale sticks in the seat, and some heater manufacturers would rather you replaced the valve on a schedule than exercised it at all.

This page is how to choose and how to do the test if you choose it. If the valve is already dripping, you are past the test. Read why the relief valve drips and do not lift the lever again to “see if it will stop.”

Read the tag before you touch the lever

The valve has a tag or a stamp with a pressure rating, a temperature rating, and a discharge capacity. The heater’s manual may say to test every so many months.

The valve maker’s sheet may say the same thing. Another manual, particularly on some storage tanks, warns that lifting the lever can deposit sediment on the seat and cause a leak that requires replacement. Both instructions exist in the market at the same time.

The one printed for your valve and your heater is the one you follow. If they disagree, replacing the valve without a home test is the conservative path, and it is a plumber’s ordinary call if you do not want to drain the tank yourself.

Look at the discharge pipe before any test. It should be full size, unterminated by a cap or a valve, sloped to drain, and ended near the floor or a receptor where a sudden spit of hot water hits nobody.

International Code Council notes on IRC P2804 explain why each of those rules exists. If the pipe is missing, capped, reduced, or aimed at your face, do not test.

Fix the pipe first, or have it fixed. A successful test through an illegal pipe is how people get burned by their own safety check. The pipe rules are collected in permits, pans, and straps.

Know where the water will go. A pipe into a pan that has no drain will fill the pan. A pipe onto a floor that drains toward a hallway will send hot water into the hall.

Put a bucket down only if you can do it without putting your hands in the discharge path. The water is at tank temperature.

The Consumer Product Safety Commission’s burn times in publication 5098 are why “a quick splash” is not a small risk. Stand to the side. Wear shoes. Do not hold the lever down while you look away.

The test itself

If you have decided the manual allows a test and the pipe is safe, lift the lever slowly until water flows, hold it only a second or two, and let it snap closed.

Do not prop it open. A healthy valve passes a burst of water and then seals. Watch for a minute. The pipe should stop dripping.

A few drops as the last water in the pipe drains are not a failure. A continued drip from the valve body is a failure. The seat did not close.

Replace the valve. Do not tap it with a hammer, do not hang a weight on the lever to “help it seal,” and do not cap the outlet until the replacement is installed.

If nothing comes out when you lift the lever, treat the valve as seized. A seized valve will not protect the tank. Replace it. Do not keep the heater in service on the theory that the pipe is clogged and the valve is probably fine.

A clogged discharge pipe is itself a danger, because the valve can open against a blockage. Someone has to correct both the valve and the pipe.

That someone should be equipped to drain the heater and to recognize a tank port that is too corroded to accept a new valve. On an old tank, get a replacement-heater price at the same time. The judgment is repair or replace.

Replacing the valve is the job you should have already agreed to before the test, if you are testing at all.

The sequence is energy off, cold water off, tank drained below the valve, old valve out, new valve of the correct rating in, with the probe reaching the top of the tank as the listing requires, discharge pipe rebuilt correctly, tank refilled and bled, energy restored only after an electric tank is full. Thread sealant has to be appropriate and must not block the valve’s internal passages.

Over-tightening cracks the port. This is a standard service call for a reason. A homeowner who has done threaded potable connections and is prepared to stop if the old valve does not come out cleanly can do it. Everyone else should not start a test on a Friday night on a tank they cannot isolate.

What the test does not tell you

A valve that opens on the lever and then seals is not proved for temperature.

You did not heat the tank to 210°F, and you should not. The lever test is a mechanical free-movement check. It does not measure whether the thermostat is accurate, whether the expansion tank is charged, or whether street pressure is too high.

A valve can pass a lever test on Tuesday and drip on Thursday because the heating cycle pushed a closed plumbing system over the pressure setting. That Thursday drip is a system problem. Diagnosing it belongs on the dripping-valve page, not to another lever test.

Do not use the relief valve as a drain for a flush. The drain valve is the drain. The relief valve is a safety device.

Every unnecessary opening is a chance to ruin the seat. Do not test the valve by raising the thermostat until it opens.

That is an uncontrolled scald and overheat experiment. The high-limit and the valve are backups, not demonstration tools.

Checklist: if you test

• Manual and valve tag both read. If they discourage a test, replace on schedule instead.
• Discharge pipe legal and aimed somewhere safe. If not, stop.
• Stand aside. Lever lifted briefly. Water flows, then stops.
• Continued drip or no flow: valve replaced, not capped.
• You already know who will replace it today if the test fails.
• Electric heaters refilled before power. Gas controls restored per the sticker.
• The expansion tank and the set point are separate questions if the drip returns during a normal recovery.

Children, pans, and forgetful levers

Do not let a child “help” by hanging on the lever. Do not tie a string to the lever so it can be operated from across the room. The lever is not a remote. In a location where a curious hand can reach it, a guard that the manufacturer allows is a conversation with a plumber, not a zip tie.

After any test, explain to the household that a puddle under the pipe is a reason to say something, not a reason to put a bucket there for the rest of the year. A bucket is how a chronic discharge hides until the valve fails open or the pan overflows into the ceiling below.

If you choose scheduled replacement instead of testing, write the date on the tag area or in the manual. Valves are cheap relative to a tank failure and cheap relative to a scald. A valve as old as a tank that is itself at the end of a 10-to-15-year service life should not be moved to the new tank “because it never dripped.”

Put a new valve on a new tank, with a correct discharge pipe, every time. The Department of Energy’s service-life range is a reminder that the safety devices age with the vessel. They are not heirlooms.

Sources

International Code Council, “CodeNotes: Water Heater Safety in the I-Codes” (iccsafe.org). IRC Section P2804 as adopted locally, for the valve and the discharge pipe. U.S. Consumer Product Safety Commission, “Avoiding Tap Water Scalds,” publication 5098 (PDF).

Valve and heater manufacturers’ own test-or-replace language on the tag and in the manual (A. O. Smith, Rheem, Bradford White, and the relief-valve makers they specify). Where those documents disagree, replacement without a lever test is the safer reading.