Water shooting out black plastic

Hi, I can’t figure out what this black plastic is, but when the pump runs water shoots out.
GP pump 4040G
Any help is appreciated.


my guess is thermal relief or high pressure relief. Is unloader not bypassing water? Is trigger gun left closed for too long?

Not sure if the Unloader is not bipassing.
It leaks wether trigger is pulled or not.

Mark is correct. Thermal relief valve. Pump is running hot. Change the pump oil and check if bypass is working.

Hmm, ok, I’ll check that then.
Thank you

It ran hot and opened to relieve the heated water before you lost the seals. It will need to be replaced or just plugged. Bypass into a tank in the future if you can. Post a pic of everything on the pump head.

What will need to be replaced?
I’ll take pics once I get to the garage, working tonight.

Replace this 0-2

Or use this in it’s place


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Why would you want to plug that @dperez ? I would think you want that valve there to help the pump…no?

Read again and you will see that it is currently defective and it’s not doing it’s job. It’s not a open/close thermostat. Once it opens it needs to be replaced or plugged.


From every post I’ve ever seen about thermal relief valve problems they fail shortly after they get triggered the first couple times. Plug it or buy a bunch of back ups… If you have an unloader and most of us should, it’ll unload before the thermal relief valve is triggered bringing in fresh, cold water.

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I didn’t know that. Thanks for explaining.

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The ports on the bottom of the head are low pressure and the ports on top will be your high pressure. So this valve being on the bottom could not be a pressure relief valve since there’s really no pressure there. You can actually even pull a vacuum on that port. Now that’s HOT lol

Pulled the bypass hose out and let water run through, no issue there.
Unless the Unloader itself is broken, I guess the thermal relief valve got triggered and just needs replacing, as stated.

@dperez Is that a 3/4 barb? Can I get that at home depot?

No, that’s not a barb/insert fitting. It’s a plug, I don’t think HD carries any hex head plugs in brass but maybe they will carry a square head plug.

I don’t know you’ll just have to check. You can also run a nipple and a cap. Just be sure to run brass only on whatever fittings you find.

And 3/8" NPT will work even though it’s most likely BSPT

Perfect, thank you

I wouldn’t plug it unless you are going to bypass to a buffer tank.

Yea, I’ll do that. Just bought a 55 gallon drum to use for sh, instead of my 100 gallon that will now become my buffer tank.

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I meant to get back to you. I was tired and made a mistake. That plug you will need should be 1/2" and not 3/8"

Yea i stopped by Lowes yesterday to pick up the plug but didn’t pull the part of the rig, so i had nothing to go by but i compared the 1/2" to the 3/8 and figured it couldn’t possibly be the 3/8". And my wife had my phone, so i just walked out the store empty handed. I’ll pull it off now and stop by home depot