Water Heater Pressure Relief Valve Leaking: Causes and Fixes

Finding water at the end of the pipe that runs down the side of your tank is unsettling. The good news is that a relief valve that drips is often doing its job. The bad news is that it is telling you something is wrong. If you need help now, our leaking water heater repair in Newark can test the system and stop the leak. This guide covers why a water heater pressure relief valve leaks, how to test it safely and when to call. It is general information, not a code ruling.

What does the water heater pressure relief valve do?

Every tank water heater has a temperature and pressure relief valve, often called a T&P valve. It is a brass valve with a small lever, near the top of the tank. A pipe runs from it down toward the floor or a drain.

The valve opens in two cases:

• Pressure inside the tank reaches about 150 psi.
• Temperature in the tank reaches about 210°F.

The valve's ratings are printed on it or on a metal tag. A probe on the valve sits in the hottest water near the top of the tank. When it opens, it lets out water or steam to keep the tank from bursting. New Castle County's replacement checklist confirms that a T&P valve and full-size relief piping are required on every replacement heater.

Why is my water heater pressure relief valve leaking?

Here are the five common causes, from most to least likely:

A. O. Smith's technical bulletin adds one more: water seeping at the threads where the valve screws into the tank. That joint can be resealed. If the leak is at the welded fitting on the tank itself, it cannot be repaired, and the heater needs replacing.

How to test why the relief valve is leaking

You can do the first checks with a hose-bib pressure gauge and a kitchen thermometer.

1. Check the valve label. It should read 150 psi and 210°F. Structure Tech notes that a boiler relief valve can look the same but opens at only 30 psi.
2. Measure house pressure. Screw a gauge onto an outdoor spigot or the heater's drain valve. Read it with no water running. Normal is roughly 40 to 80 psi.
3. Watch pressure while the heater runs. Leave the gauge on for a heating cycle. Some gauges have a red "lazy" needle that marks the highest reading. If it climbs toward 150 psi, the cause is pressure.
4. Check the water temperature. Run hot water at the nearest tap for a few minutes and measure. Water near the boiling point means a thermostat problem. Shut off power or gas and call.
5. Check for an expansion tank. If you have a check valve, pressure reducing valve or backflow preventer and no expansion tank, that is your likely cause.

Never cap or plug the relief valve or its pipe to stop a drip. That removes the tank's last line of defense.

What causes thermal expansion leaks?

When water heats up, it expands. If a one-way valve at the meter keeps it from flowing back to the street, pressure rises fast. The 2021 International Plumbing Code, which Delaware adopted in 2022, requires a thermal expansion device on storage heaters in that setup. Our guide to the water heater expansion tank explains how it works and how to size one.

An expansion tank can also fail. A waterlogged tank or one that has lost its air charge acts like no tank at all, so the drips return.

How to fix a leaking water heater pressure relief valve

The fix depends on what the tests showed:

• Pressure spikes during heating: add an expansion tank, or recharge or replace the old one.
• High pressure all the time: install or reset a pressure reducing valve so house pressure stays under 80 psi.
• Normal pressure and temperature, still dripping: replace the T&P valve. Use a valve with the same or lower pressure rating and the correct heat input rating for your heater.
• Water too hot: lower the setting or replace a failed thermostat or gas control.
• Leak at the valve threads: remove the valve and reseal the joint.

Replacing the valve means shutting off the water and heat, draining some water, removing the old valve and threading in the new one with sealant. Then refill, check for leaks and restore heat. Because hot water and gas lines are involved, many people leave this to a pro.

Is a leaking relief valve dangerous?

A slow drip is not an emergency, but it is a warning. Treat it as urgent if:

• Hot water or steam is coming out
• Water is flowing steadily, not dripping
• The tank makes loud rumbling or popping noises at the same time
• The discharge pipe is missing, capped or runs to a spot where water could hurt someone

In those cases, turn off the gas or power and the cold water supply, then call. Our guide on whether a leaking water heater is dangerous covers the full safety checklist.

Testing the relief valve as maintenance

Most water heater manuals say to lift the test lever once a year. Put a bucket under the discharge pipe, lift the lever briefly and let it snap back. Water should flow, then stop.

Be ready for one side effect. On older valves, mineral grit can keep the seat from closing after a test. If that happens, lift and release it a few more times. If it still drips, replace it. That is better than finding out in an emergency that the valve is seized.

Newark and Delaware relief valve notes

• Discharge piping rules. New Castle County's self-certification checklist requires full-size relief piping on replacement heaters. The pipe should end where water can be seen and will not hurt anyone.
• Hard water. Newark-area water is moderately hard, so mineral buildup on valve seats is common. A valve that has sat untested for years may stick.
• Closed systems are common. Many homes have backflow protection at the meter, which makes thermal expansion the top cause of drips.
• Wasted water adds up. A valve that drips into a floor drain can raise your bill for months. See why is my water bill so high?

How to prevent relief valve leaks

• Keep house pressure under 80 psi and check it twice a year.
• Install and maintain an expansion tank on any closed system.
• Set the heater near 120°F. See water heater temperature setting for how.
• Test the valve yearly and replace it if it sticks.
• Flush the tank yearly to limit sediment and mineral grit.

Local note: In Pike Creek and Hockessin, many heaters sit in finished basements or closets, so a dripping relief valve can soak flooring before anyone sees it. Check the end of the discharge pipe whenever you change a furnace filter.

Related reading: Find other leak sources with why is my water heater leaking?, and if the heater is old, weigh your options with signs your water heater is going out.

When should you call a water heater professional?

Call a pro if:

• Hot water or steam comes from the discharge pipe
• House pressure reads over 80 psi or spikes during heating
• A new valve starts dripping again within weeks
• Water is seeping where the valve meets the tank
• The discharge pipe is missing, too small or capped

Water heater pressure relief valve leaking in Newark? Call (302) 732-0874 for leaking water heater repair from Newark Heater Pros.