Water Heater PRV Leaking: Causes & Fixes

1. Water pressure is too high

The pressure relief valve (PRV) is designed to open and release water when system pressure exceeds its rated limit (typically 150 psi). If your incoming water pressure is consistently too high, the valve will discharge regularly—and appear to be leaking.

1. Turn off power to the water heater (circuit breaker for electric; gas valve to “pilot” for gas).
2. Attach a water pressure gauge to an outdoor hose bib or the cold-water inlet on the heater.
3. Read the pressure. Normal range is 40–80 psi. Above 80 psi is too high.
4. If pressure is high, locate your home’s pressure-reducing valve (PRV) on the main supply line, usually near the water meter.
5. Turn the adjustment screw clockwise to lower pressure, checking the gauge until you reach 60–70 psi.
6. If no pressure-reducing valve is present, or yours is faulty, have a plumber install or replace one.

2. Water temperature is set too high

When water temperature climbs too high, thermal expansion increases pressure inside the tank, triggering the PRV to open. Check your thermostat setting as a quick first step.

1. Turn off power to the heater before touching any components.
2. For an electric heater: remove the access panel(s) on the side of the tank. You will see one or two thermostats behind insulation. Use a flathead screwdriver to adjust each thermostat to 120°F (the recommended setting per U.S. Department of Energy guidance).
3. For a gas heater: locate the dial on the gas control valve near the bottom of the tank and turn it to the “Hot” setting, which corresponds to approximately 120°F.
4. Restore power and wait 30–60 minutes for the water to reheat.
5. Monitor the discharge pipe at the PRV. If it stops dripping, the high-temperature setting was the cause.

3. Thermal expansion with no expansion tank

In a “closed” plumbing system (one with a backflow preventer or check valve on the main line), heated water has nowhere to expand except into the tank, raising pressure and causing the PRV to weep. An expansion tank absorbs that excess volume.

1. Confirm whether you have a closed system by asking your municipality or checking for a backflow preventer near the water meter.
2. Inspect the area near the cold-water inlet on your water heater. A thermal expansion tank, if present, will be a small tank (often red or blue) teed into the cold-water supply line.
3. If no expansion tank is present, contact a licensed plumber to install one—this is often required by code in closed systems.
4. If an expansion tank is already installed, check its pre-charge pressure with a tire gauge on the Schrader valve at the top. It should match your cold-water supply pressure (typically 50–60 psi). Use a bicycle pump or air compressor to correct if low.

4. Water heater PRV leaking due to a faulty or old valve

Over time, mineral deposits, corrosion, or a worn internal spring cause the relief valve itself to leak even when pressure and temperature are normal. A PRV older than 3–5 years should be tested and potentially replaced.

1. Place a bucket under the discharge pipe connected to the PRV.
2. Lift the test lever on the PRV for 2–3 seconds, then release it. Water should flow freely and stop completely when you let go.
3. If the valve continues to drip after you release the lever, it is faulty and must be replaced.
4. Turn off the cold-water supply to the heater and turn off power (or set gas to “pilot”).
5. Open a hot-water faucet in the home to relieve pressure, then attach a garden hose to the tank drain valve and drain several gallons until the water level is below the PRV.
6. Use a pipe wrench to unscrew the old PRV. Wrap the threads of the new valve with plumber’s tape (PTFE tape), then thread it in hand-tight and snug with the wrench—do not overtighten.
7. Reconnect the discharge pipe, turn water back on, restore power, and check for leaks.

5. Loose or corroded discharge pipe connection

Sometimes what looks like a leaking PRV is actually a weeping joint where the discharge pipe connects to the valve outlet. Check the fitting before replacing the valve itself.

1. Visually inspect the threaded connection between the PRV outlet and the discharge pipe for mineral staining, corrosion, or drips originating at the joint rather than the valve seat.
2. Turn off water supply and power/gas to the heater.
3. Use a pipe wrench to gently tighten the discharge pipe fitting. Do not over-tighten—brass threads strip easily.
4. If the pipe is corroded or the threads are damaged, remove the pipe, clean the threads, apply fresh PTFE tape, and reinstall.
5. Restore water and power, and watch the joint for 10 minutes to confirm the leak has stopped.

6. Sediment buildup causing pressure spikes

Sediment that accumulates at the bottom of the tank can cause localized overheating (hot spots), leading to intermittent pressure spikes that trigger the PRV to open. Flushing the tank annually prevents this.

1. Turn off power to the heater (circuit breaker or gas valve to “pilot”).
2. Connect a garden hose to the drain valve at the base of the tank and run the other end to a floor drain or outdoors.
3. Open a hot-water tap in the home to break the vacuum, then open the drain valve.
4. Let the tank drain for 10–20 minutes or until the water runs clear and free of sediment.
5. Close the drain valve, remove the hose, close the hot-water tap, and restore the cold-water supply.
6. Once the tank is full (water flows steadily from the open hot-water tap), restore power or relight the pilot.
7. Repeat this process once a year to prevent recurrence.

Frequently asked questions