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Thread: Boiler pressure relieve valve leaking

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    DIY Junior Member Arepa's Avatar
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    Question Boiler pressure relieve valve leaking

    Hey guys,

    I have this boiler with a coil for domestic hot water. Once the pressure relieve valve started to leak I replaced it right away since it was at least 15 years old. That did not resolve the problem, so I checked the expansion tank, model 110, and there was no air at all in there. I pumped 12 PSI of air as it comes from factory, the tank holds the pressure fine, but the valve still leaks. For kicks, I pressurized the tank to 30 psi and the valve still leaks!!! That is with the boiler off, so that is just from the water pressure of a well which has very little pressure... The expansion tank is about 15 years old. I think there is a 3rd thing I could look into on this situation but I cannot remember... Any suggestions would be greatly appreciated.

    Steven

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    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    What is the pressure on the boiler? Your pressure reducing valve that feeds the boiler can also be bad.

    John

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    DIY Junior Member Arepa's Avatar
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    Quote Originally Posted by johnjh2o1 View Post
    What is the pressure on the boiler? Your pressure reducing valve that feeds the boiler can also be bad.

    John
    If I am reading that gauge correctly, it is 35 PSI... and I do not see an adjustment on the pressure reducing valve. How much pressure should the water on the boiler have?

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    DIY Junior Member Arepa's Avatar
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Size:  35.3 KB Here is a pic of the reducing valve I have... I cannot tell the brand, I know that the watts brand is very simple to adjust the pressure by losing the bolt, and turn the top section. Anyone knows if this one can be adjusted and to what value? Thanks

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    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    It's adjusted by loosing the screw in the top. But they don't just go out of adjustment. But they do fair and need to be replaced. According to your temperature gauge the boiler is off. If it is off the high pressure shows that the problem is in the feed valve. The pressure relief valve is doing it's job.

    John

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A typical boiler operating pressure for a residential system is in the area of around 12-16psi (around one atmosphere). Some need more, but look at the relief valve, it's probably a 30psi version - a 2x safety factor is pretty common. It's pressurized to prevent the boiler water from boiling in the heat exchanger.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    First, turn the filler valve for the heating system fully off. (I never rely on the auto-fill systems at my house- YMMV- you'll hear the sizzle & bang from low pressure long before it's a hazard or damaging). Bleed water on the heating system until the pressure is about 12-15psi- note the pressure carefully. Check it again in 24-48 hours. If it's climbing over time back up to the 35psi level, you have a leak between the potable and heating system side of the hot water coil.

    If it's leaking, rather than replacing the coil, install an indirect-fired tank for the hot water operated as a separate heating system zone, capping the ports to the coil. You can then lower the standby temp on the boiler to save money (which would be considerable, if oil or propane.) It's safe to use 130F as a low-limit for gas, 140F for oil. Most newer gas boilers can be cold-fired without damage, but some older units might have leakage issues when cold. Some newer oil-boilers can be cold-fired, most older units not, but unless the flue has a stainless liner, cold-firing just for HW heating calls in summer can lead to damaging levels of acidic-exhaust condensation on ceramic-lined flues.

    When installing an indirect on an older boiler, it's worth installing a heat-purging fuel economizer (eg. Intellicon 3250 HW+ ) which minimizes standby loss on the boiler by always parking it at a lower temp at the end of a burn, and taking it to the (programmed) low-limit before firing on during a new call for heat.

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    Engineer MichaelO's Avatar
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    Arepa,

    I'm also a homeowner, not an HVAC tech. Regardless, I've experienced a pressure reducing valve failure, and it didn't just fail outright: it became inconsistent, over pressure one day, no pressure the next...

    Regards,
    Mike O'

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