Pressure Relief Valve


Old 08-13-08, 12:26 PM
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Pressure Relief Valve

The pressure relief valve on my hot water boiler is activated occasionally causing a five gal. pail to fill up approximately every 2 weeks. The relief valve has been replaced and the expansion tank was drained before the start of the heating season. The pressure guage on the boiler does indicate the pressure is close to the rating of the relief valve. The expansion tank is a 25 gallon tank non-diaphram type. Thanks for any assistance on this matter.
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Old 08-13-08, 05:15 PM
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Doug, there's a few reasons this might be happening...

first, it's possible that the tank wasn't completely drained because of a 'vacuum lock' condition. Sorta like when you put your finger over the end of a drinking straw and lift it out, the liquid stays in the straw. That's the first thing I would check.

second, your water feed valve may be slightly hanging open, and continuing to feed water and over pressurizing the system. When you get the pressure to 12-15 PSI, try turning the manual shut-off ahead of the feed valve OFF for a while and see if it still blows the relief valve. OR, it's possible that the feed valve is simply mis-adjusted or otherwise defective.

What is the pressure on the system when it's cold ?

third, if you are making domestic hot water by means of a coil inside the boiler with your system, it's possible that coil has sprung a leak and is feeding water into the boiler...

If you have a standard expansion tank, you should not have any automatic air vents on the system. If you do, the system will slowly lose the air in the expansion tank and the tank will waterlog.

Pics might be helpful for further diagnosis...
Old 08-15-08, 06:29 PM
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Trooper, I am just going to add a little to this. Hope you don't mind.

Just for giggles, What are the pressure and temperature readings on the gauge when it is HOT (when the boiler turns off), and COLD, (when boiler turns on.)?

Pressure readings combined with temperature readings will tell us a lot.

Does the leak happen all the time or only when the boiler is up to temp?

Sounds like an expansion tank problem, but we wont know without more info.

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