I moved into my house a few years ago and did not realize I needed to occasionally test my hot water heat relief valve. I had never tested it before today. I also have never had any problems with it. It is a Whirlpool 40 gallon tank with a max working pressure of 150 psi. My house does not have a regulator or expansion tank so whatever pressure is in the city line is what my house gets (I think).

I tested it for the first time today. Before doing so I isolated it from the gas feed and the water inlet feed. It spurted out some blackish dirty looking water and then stopped. I closed it and reconnected all the lines and now it has a slow trickle out of the relief valve. I tried running the hot water out of several faucets for awhile but the leak continues. It did not leak before I tested the valve.

Any thoughts on what might be going on here?

3 Answers 3


That black gunky stuff is in the relief valve's valve seat now, so it can't close completely and it leaks. It needs to be flushed out.

With the cold water supply turned on, squirt more water out of the relief valve and try to get a few spurts at a decent flow from it. The water will be hot, so use caution. The leak should stop. If it does not, the valve should be replaced.

  • Well I tried. At least one of the times I had it open the leaking seemed to get worse. I also noticed leaking/drips at the actual little valve handle itself. I did it a few more times and now the leaking is back to what it was.
    – Nukesub
    Jun 25, 2022 at 19:40
  • 1
    @Nukesub You may be able to take the valve off the water heater, take it outside, open it fully and give it a good blast with a garden hose to clean the seat, stop the leak and get a few more years out of it, but if you're taking it off and reinstalling it, maybe it's time to just replace it and be done with it.
    – MTA
    Jun 25, 2022 at 19:47
  • Thanks - I replaced it. Leak is gone.
    – Nukesub
    Jul 6, 2022 at 2:23

A few years plus the time before, it might just be easier to replace the valve.

Turn off the heater, turn off the cold water inlet. Open a hot water tap/faucet upstairs/above. Drain water from the tank till no more water comes out of the pressure valve. Tank should be drained a bit every month or two also to remove sediment.

Replace the valve. Turn on cold water inlet and leave the hot water tap open till no more air comes out. Turn on heater and you should be good to go.


It is recommend to completely empty and clean the water heater at least once every 2 Years.

The reason is to remove the junk/slurry build up, that will effect the heating coil and limit its life.

Turn off the power or gas.

Let someone use long shower, so not to waste hot water.

Turn off the cold water supply.

Open the valve at the bottom of the heater to drain it (with hose attached) to it to lead it away. Do not close it just yet.

Open the cold water supply, open a faucet closest to near it.

Leave the Overpressure valve open to flush it, cycle it on off, to clean the seal.

Close faucet and drain but leave the overpressure open for a while.

That is to flush the heater util clean water comes out.

When clean water is coming out everywhere, close all.

Power on.

  • Thanks - I will give that a shot. I need to get a replacement valve though. Mine is a Watts L100XL-3M7 which is a 3/4" extended shank valve with 150 psi relieving pressure. No places around me have this specific model but they have larger ones meant for water heaters with thicker insulation. Do you have any idea how you determine what the insulation thickness of a water heater is? My installation manual does not say and the Whirlpool model number did not yield any meaningful results.
    – Nukesub
    Jun 28, 2022 at 1:12

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