Need help with leaking pressure relief valve


Old 06-17-10, 11:44 AM
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Unhappy Need help with leaking pressure relief valve

I've been reading other posts but can't seem to figure this out.

I have an indirect-fired hot water heater. Boiler & hot water heater are Weil Mclain installed in 2003. The 30 psi pressure relief valve is leaking.

30 psi Pressure Relief valve has been replaced, still leaking.

Replaced pressure reducing fill valve, still leaking.

Expansion tank checked and pressure at ~12psi. Top has water, bottom sounds hollow. This is the "gas grill" looking type.

Gauge on boiler shows pressure at 30psi but the gauge is now filled with condensation and no longer goes below 30psi, even if I turn off incoming water to boiler and manually release the relief valve. This used to bring the pressure on the gauge down, but now it doesn't anymore. So I guess the gauge is suddenly broken?

So far nothing has stopped the leaking pressure relief valve.

I can provide more info or pics if that will help, just let me know and I'll be glad to post more info. Thanks so much for any help you can provide.
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Old 06-17-10, 12:15 PM
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I'm no expert but I do know that to check the pressure of the expansion tank it must de-pressurized on the water side or completely removed from the system. Did you do this ?
Old 06-17-10, 12:29 PM
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Thanks for the reply. I think I turned off the valves around the tank. The fact that is was at the correct PSI leads me to believe I did it correctly, otherwise wouldn't it read too high?
Old 06-17-10, 01:10 PM
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Leaking relief valve

If the expansion tank has no charge in it, the pressure reading will be whatever the system pressure is.
Old 06-17-10, 01:25 PM
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You should shut off the make-up water, and drain the system pressure down to zero before checking the air pressure in the tank.

I'm wondering if you have a pinhole in the indirect hot water heating causing the pressure to rise.
Old 06-17-10, 02:23 PM
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What they said... if you don't depressurize the boiler, you will not read the correct pressure on the air side.

Here's a 'step by step' that should get you where you need to be with the expansion tank.


1. Shut off boiler and allow to cool to under 100F.

2. Shut off water supply line to boiler.

3. Drain only enough water from the boiler drain to drop the system pressure to ZERO. (do NOT completely drain the boiler!)

4. With an ACCURATE tire pressure gauge, check the air charge in the tank on the air valve opposite the end of the tank that's connected to the system. If ANY water comes out of the air valve, the bladder inside the tank is shot and the tank needs replaced. If no water comes out the air valve, and the pressure is less than 12-15 PSI, continue to step 5. If the pressure is OK, turn the water supply to the boiler back on and repressurize the system, turn the power back on to the boiler, no service is necessary.

5. Using a bicycle pump, or a small air compressor, add air to the tank until you have 15 PSI air charge.

6. Check the boiler pressure gauge again, and if it has risen off ZERO, drain some more water from the boiler drain until it is again at ZERO.

7. Check the air charge on the tank again. If it is below 15 PSI, add air to the tank until it is at 15 PSI.

8. Repeat steps 6 and 7 until the boiler stays at ZERO and the tank stays at 15 PSI. At this point, the tank is properly recharged and the water supply can be turned on to re-pressurize the system, turn the power on to boiler and return to service.


Since your boiler gauge is pooched, you should plan on replacing that. Without being able to know the pressure in the boiler, yer stuck, it's all guess work...

You can purchase fittings to adapt a pressure gauge to a boiler drain fitting. Purchase a gauge that has a 0-30 PSI range. Screw the thing onto the drain, open the drain, and read the pressure.

You can buy a gadget pre-made for about $10 at HD or Lowe's that sprinkler dudes use to measure pressure. Screws onto hose fitting... BUT the gauge it comes with is useless for boiler work, as they are like 0-200 or 0-300 range. But for $10 you can buy that, unscrew the gauge it comes with, and screw a different one on there.

Aside from plumbing supply houses, a good source for gauges would be a pool supply house. HD and Lowes probably don't have a suitable gauge on the shelf.

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