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Old 12-16-2012, 09:14 AM   #1
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How to change a bad pressure relief valve

I have an Oil fired hot water heating system. The pressure relief valve on top of the furnance or boiler is leaking. I found the valve to shut off the incoming water supply from the well to the boiler.

Before I remove the valve to replace it, must I drain down the system. There is a boiler drain valve at the base of the boiler. How much water must I remove from the system, or can I just shut the water intake valve, let it cool down & remove the valve? I'm not sure how to do it. Also I assume when I refill the system, any air in the water lines will exit out the puge valve that is mounted at the water inlet valve.

The pressure valve that's leaking is a Watts No 335 Size 3/4" Set 30 lbs BTU per hour rating. ASME 510.000 I assume I need to find the same replacement at the plumbing supply. Thanks for the help everyone.


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Old 12-16-2012, 11:53 AM   #2
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Unless the shutoff valve is leaking, there's no reason to drain the boiler. Shut down the boiler, let it cool, then manually lift the relief. If the shutoff is holding, you should get little to no water coming out. With a wrench, unscrew the old valve and screw on a new one.

The ASME Boiler and Pressure Vessel Code is quite strict in its requirements, so be sure you purchase exactly the same valve.


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Old 12-16-2012, 02:53 PM   #3
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Ayuh,.... Are ya Sure it's Bad,....

A bad pressure tank, can cause that valve to leak also...
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Old 12-17-2012, 12:46 PM   #4
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Thanks for the advice. I picked up a new pressure relief valve and it is made by the same company as the original & the operating specs are the same. The old valve definetly is weak. It is leaking a little & if I press down on the top of the valve I can stop the leak.When the heat is on, I do get some leaking so I have a bucket under the blow off pipe to catch the leak.

I was thinking that if I remove the valve without draining down the system, I would cause a flood, but I guess not if the water in the system is cold. Anyway, I will change out the valve, probably tomorrow when I have time to do it. Right now I have a 3 gallon bucket to catch the leak water & it takes about 14 hours to fill the bucket. So It's not a real large leak but by tomorrow I should have the new valve in & problem solved. Thank you all for the advice & help.
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