Boiler dripping water out of pipe from pressure relief valve


Old 11-17-13, 04:25 PM
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Boiler dripping water out of pipe from pressure relief valve

I had some problems with my boiler last week but I think I resolved them with NJ trooper's help. Here is the thread

Tonight I heard a loud bomb and I ran downstairs to see hot water on my basement floor.
It looks like the pressure relief valve opened and then closed but released about a gallon of water. Not the pipe to the valve has a slow drip.

I've been checking the pressure of the boiler and the pressure has been around 30psi while it's running and about 15 psi cold.

Do you recommend replacing the pressure relief valve since it's still dripping or does it take a while for it to reseat?

I'm more concerned on why the valve opened but I will continue to keep an eye on the boiler pressure.

I've attached some pics of the valve, gauge and piping.


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Old 11-17-13, 04:55 PM
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I guess I should have warned you that was going to happen, eh?

Sorta did... by saying in the other thread:

You should have 12-15PSI on a COLD boiler and maybe as much as 10PSI higher when hot.
But I suppose I didn't stress that fact as much as I should have.

When you saw pressure up near 30 PSI, you should have told us then!

OK, since the relief valve is obviously more than 5 years old, you should plan on replacing it. Even when you get the pressure under control it will probably still leak.

You also need to COMPLETELY drain your expansion tank.

To do this, you need to connect a drain hose to the faucet in this picture:

Shut the boiler off and close the red valve in this picture:

Open the drain with the hose and let ALL the water out of the tank.

When you open that valve, water will flow and then stop... BUT, the tank is NOT EMPTY YET! This is because of the 'drinking straw analogy'. Put your finger over a drinking straw and lift it out of the drink. Stays in the straw.

Same thing happens when you drain that tank. It will pull a 'vacuum' inside.

At this point, close the valve, disconnect the hose and put a bucket under the drain and open it. The tank should take a gulp or two of air and the water will flow again.

Hook up hose again and drain until it stops again... and repeat with the bucket.

You may have to do this a number of times.

Sometimes leaving the hose connection to the valve LOOSE so that some air can get sucked in will help.

If you have a hose "Y" connector handy,

image courtesy

you can use that on the tank drain so you don't have to keep removing the hose.

Do you own a small air compressor? If so, and you can rig up some way to pump air into the tank it will speed the process. I have found that old washing machine hoses are just the right size to shove my air nozzle into and force air into the tank. Don't go crazy with the pressure, you only need about 20 PSI or so.

Basically, whatever you have to do to get that tank drained is what you have to do.

Once it's drained, close the drain, open the red valve, and you should hear your feed valve adding water to the system. The tank will partially refill about 1/2 way and compress the air that is now in the top of the tank.

Now when you run the boiler the cold pressure should still be around 12 PSI but the pressure when the boiler is HOT should not be more than 20+ PSI.
Old 11-18-13, 05:11 AM
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Location: usa
Posts: 11
Thanks NJ Troop.
I'mg going to drain the tank this morning.


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