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Thread: Leaking Indirect coil causing Boiler Pressure to increase= pop of t+P

  1. #16
    DIY Junior Member bluefleetwood's Avatar
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    Quote Originally Posted by Dana View Post
    28psi is bumping pretty close on 30psi. Sounds like the expansion tank on the heating system may be marginally sized or not correctly pre-charged. You should set the system at 12psi when the boiler is cold.

    What type of heat emitters and piping do you have (other than the hydro-air coil on the second floor)? Big high-volume radiators need much bigger expansion tanks than fin-tube baseboard, due to the high volume. If the original expansion tank was marginally sized and failed, this one will too.
    I have Hydro for the first floor as well.
    3 zones, Hot water, First and second floor. New expansion tanks on both hot water and boiler.
    I had to change them about 2 months ago as both will filled with water.
    Last edited by bluefleetwood; 05-30-2013 at 04:40 PM.

  2. #17
    In the trades Dana's Avatar
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    You changed the expansion tanks, but did you pre-charge them for the right system pressure when you installed them?

  3. #18
    DIY Junior Member bluefleetwood's Avatar
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    They came precharged. Should I have checked it? Tire Gauge? What should they be charged at?

  4. #19
    Retired Defense Industry Engineer jadnashua's Avatar
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    They may or may not actually have the proper air pressure in them. You check them with a stock tire pressure gauge. A compressor may be hard to get the exact pressure you want, so something like a bicycle pump may work well. The air pressure IN the system will equal the water pressure, so to check the precharge, you must relieve the water pressure in the system, leave a valve open, then precharge the tank to the normal working pressure of the system it's attached to. For the house, that would be where you have the PRV set to. For the boiler, that depends on your normal working pressure, often about 1 atmosphere, or around 14#, but it could be more. IF the ET doesn't have the proper precharge, it stresses the bladder and, may not hold the designed amount of water created during heating.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #20
    In the Trades Tom Sawyer's Avatar
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    They come pre charged at 12lbs. In thirty years I have seen maybe 2 that were not properly charged. In 30 years I think I have had to re-charge maybe a half dozen. I very much doubt the problem lies with the tank unless its not big enough.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  6. #21
    DIY Junior Member bluefleetwood's Avatar
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    I really appreciate all of this input.
    My current status is:
    Boiler pressure still between 20 and 28 PSI. Auto-fill still off. 30PSI Pressure Relief Valve Still dripping.
    Assuming a pin hole in the Water Heater, should not the pressure in boiler approach domestic pressure? Or is the PRV preventing that?
    I was replacing these PRV's so often that I've install a valve between it and the boiler as not to have to drain the whole system for replacement.
    Question, if I close that valve, will I then see pressure increase towards the domestic pressure because there is no PRV at this point?
    Hmmmm?

  7. #22
    In the Trades Tom Sawyer's Avatar
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    Shut off the water to the water heater, drop the boiler pressure to 12 lbs and wait. If the pressure stays at 12 lbs the water heater is leaking.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  8. #23
    DIY Junior Member bluefleetwood's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    Shut off the water to the water heater, drop the boiler pressure to 12 lbs and wait. If the pressure stays at 12 lbs the water heater is leaking.
    OUTSTANDING!!!!!!!!
    Thanks Tom.
    Conducted that experiment this morning. Turned off domestic feed to Hot Water Heater and opened a hot side faucet to relieve pressure. Watched the boiler pressure go to 12!
    Funny thing though, When I turned the domestic back on, it blew out the PRV violently. Guess I opened it too fast.
    YOU GUYS ARE THE BEST!!!!!!!!!!!!!!
    WISH I HAD YOU HERE TO SWAP IT OUT!

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