Leaking pressure relief valve on boiler

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  #1  
Old 12-27-08, 06:32 AM
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Leaking pressure relief valve on boiler

The relief valve on my boiler is leaking. I replaced it yesterday after I found a bunch of crud in the old leaking valve. The new one is now dripping.

The temp in the boiler is 180F and the pressure is 28-30 psi when hot and near 0 when cold. The water supply to the boiler is regulated to 12 psi. The water temp was near 200 so I turned it down in an attempt to lower the pressure. That did not help.

The system was installed in 1998 and has a diaphragm expansion tank.

I believe the leaking is due to high pressure when the boiler is heating. It makes me suspect something is wrong with the expansion tank

Here's my questions:
How can I regulate the pressure during heating?
What temp should the water be set?

Thank you
John
 
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Old 12-27-08, 08:00 AM
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There must be a problem with the expansion tank - either insufficient air or a bladder leak. You can first drain the water side of the tank, and then pump 12 psi air into the bladder side with a bike pump.

The relief valve is likely set for 30 psi. So, if the system pressure gets near that, it will discharge or weep.
Doug
 
  #3  
Old 12-27-08, 08:55 AM
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Doug, thanks for the reply

I didn't think there was an air valve on the expansion tank so I got up on a step ladder and found the air valve! It was in a depression on the top of the expansion tank and couldn't be seen from the floor.

I checked the pressure in the expansion tank and found it to be 28. I relieved the pressure in the system and pumped it up to 45, then lowered it to 16. I'm not sure my pressure gauge is accurate that low and didn't want it too low.

You said to drain the water side. Did I do that correctly by pumping the expansion tank pressure up to discharge the water?

I just ran the boiler through a heating cycle. The pressure gets to 22. I hope this will prevent the relief valve leak. I'll give it a while so the exhaust pipe can dry.

Now my other question, what temp should I set the aquastat?

John
 
  #4  
Old 12-27-08, 09:25 AM
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John, you can't check the air pressure in the tank with any pressure on the boiler water side of that tank. You will not get an accurate reading.

You first need to drain ONLY ENOUGH WATER TO GET THE BOILER TO ZERO PSI . THEN check the air charge. You read 28 PSI because that's the pressure in the boiler ... if you have pressure in the boiler on a tank, and that pressure is HIGHER than the air charge, you will read the higher of the two pressures.

So, first get to zero on the boiler. Then check the air charge.

DON'T pump the tank up to 45, even temporarily... might stress that old tank and CAUSE a leak in the bladder... 12-15 PSI is fine... 16 is OK if that's what's really in there...
 
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Old 12-27-08, 10:17 AM
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NJ Trooper, I should have known that I was measuring the system pressure. That's what happens when I'm getting old!

I did adjust the air pressure the way you described. I thought it would be safe to get to 45 because the tank says max pressure is 100. I hope I didn't do it any harm.

What temp should I set my boiler?

Thanks
John
 
  #6  
Old 12-27-08, 12:27 PM
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John, I doubt you did any damage... they are rated for a much higher pressure... just on an old bladder I wouldn't stress it that much is all... just like us old dudes, two beers max... Beer 4U2 ...before the relief valve opens...

Typically the high limit on the boiler aquastat is set to 180F.
 
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