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Thread: pressure reducing valve vs boiler fill valve

  1. #1
    DIY Member philtrap's Avatar
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    Question pressure reducing valve vs boiler fill valve

    Folks,

    I used a Taco Cartridge Pressure Reducing Valve for my new Boiler. Is there a difference from that valve to a boiler fill valve? I seem to think they work slightly different and I may have used the wrong valve to for the fresh water. Plus my pressure in the system started at 12 and gained 2 psi every day without even firing the boiler up. The system is fully bled of air and I ran it for a while and the pressure went to 21psi so I shut it all down and let it sit for days and released the pressure to 12 and left it off and thats when it started to creep up each day. It's been 3 days and it went from 12 psi to 16 psi without running.

    I got a new expansion tank charged and checked to 12psi before installation...

    I'm thinking the PRV is not the right type and will replace it but that;s why I'm asking if there is a difference between the two types.

    Thanks,

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    If it's what I think you have, it may be defective. When operating properly, it should only open when the pressure in the closed boiler loop drops below its setting. It sounds like it is leaking a bit.

    Two things, an autofill valve like that will mask a system problem with a leak, but it will keep the boiler operating because it should never get below the low-pressure cutout safety switch. Second, many times, they'll install a ball valve before the autofill, so they can shut off its function, and it only really gets used when you need to drain and then refill the system after maintenance or repair.

    It is not good to regularly be adding fresh water to a boiler loop...fresh water has oxygen and dissolved minerals in it. Once the water has been there awhile, it becomes fairly inert, but that extra oxygen means it can react with any metals that can rust...you really want to keep that out!
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the trades Dana's Avatar
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    The Taco Cartridge Pressure Reducing Valve is an appropriate part for the application- it's function is no different from what other vendors call an auto-fill valve.

    Whether that's the source of the leak causing the slow rise in pressure is something that needs to be investigated, since leaks in indirect water heater heat exchangers or tankless coils embedded in the boiler can have a similar system. If you turn kff the isolating valve that feeds the Taco PRV and the pressure still rises, it's not a leaking PRV.

  4. #4
    In the Trades Tom Sawyer's Avatar
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    Quote Originally Posted by Dana View Post
    The Taco Cartridge Pressure Reducing Valve is an appropriate part for the application- it's function is no different from what other vendors call an auto-fill valve.

    Whether that's the source of the leak causing the slow rise in pressure is something that needs to be investigated, since leaks in indirect water heater heat exchangers or tankless coils embedded in the boiler can have a similar system. If you turn kff the isolating valve that feeds the Taco PRV and the pressure still rises, it's not a leaking PRV.
    Phil's system is brand new. It's probably a defective reducing valve but you don't need it anyway. Run the pressure up to 12 lbs and shut the feed valve off. Pressure should stay within a couple of pounds.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Member philtrap's Avatar
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    Thanks Tom. I wasn't aware that it's OK to run the system with the supply shut off? If I do this do I need to turn it on once and awhile to top off the system or once the system is charged it should be good for a long time?

  6. #6
    In the Trades Tom Sawyer's Avatar
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    Phil, we stopped putting auto feeders on when the code started to require a back flow preventer and having it piped to a drain. There's no reason to leave the valve to it on once the system has been filled, purged and run for a few hours. Your boiler has a low water and a low pressure sensor that will shut it down if the pressure drops below, IIRC about 6 lbs. so fill it, purge it, run it and then shut off the fed valve.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If the pressure drops, you have a leak you need to find. Did you read and understand post #2?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Member philtrap's Avatar
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    Thanks again Tom for all your help.

    Thanks too Jim. I did read your previous post and do understand it. I'm 99.9% sure now after shutting the main supply valve off and not seeing any increase that it's the auto fill PRV. I have a feeling I overheated the PRV when sweeting it on. I was going to replace the guts that may be damaged, but not from the posts above that I really don't need it, I'll just leave it alone.

    I do have a back flow preventer.

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