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Pressure loss in radiant system

scrantch
scrantch Member Posts: 38
Is it normal to lose pressure when system is off? It reads about 10 lbs cold and when the the heat is on it goes to about 28lbs. It used to stay more constant, like 18 lbs when originally set up.

Comments

  • Dave T_2
    Dave T_2 Member Posts: 64
    classic symptoms of defective expansion tank.
  • scrantch
    scrantch Member Posts: 38
    Thank God I thought there may have been a leak in the pex in the slab
  • hot_rod
    hot_rod Member Posts: 15,023
    if only that green handled ball valve would have been below the tee :) That would make for a quick and easy tank removal check or replacement.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • scrantch
    scrantch Member Posts: 38
    I know another plumber said the guy must have been stoned when he set up this system.
    SuperTech
  • scrantch
    scrantch Member Posts: 38
    What do I do, stick my finger in it while I screw the new tank on with one hand? Antifreeze dripping everywhere.
  • hot_rod
    hot_rod Member Posts: 15,023
    scrantch said:

    What do I do, stick my finger in it while I screw the new tank on with one hand? Antifreeze dripping everywhere.

    Yeah, it's never pretty changing out or removing a tank, especially if it is waterlogged.
    I slip a 5 gallon bucket over the tank, lossen the thread and let it dribble into the bucket.
    It will be heavy!

    I'd remove the tank and have an iso valve all doped up and ready to go. That will be easier to screw in, compared to a tank. Now you have a quick connection, and an iso valve for the next guy.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    scrantch
  • Dave T_2
    Dave T_2 Member Posts: 64
    @hot_rod nailed it. Shut off the feeder and be sure to attempt this after the boiler has cooled off to a temperature that cannot harm you (colder the better). IF diy do it 1st am on middle of the week in case you need to call in help. If you shut off feeder (green handle valve above tank) and turn off boiler, most of the pressure will drop as it cools off.
    Remember - any water that is lost (including most of the waterlogged tank) will need to be replaced and this is going to dilute your antifreeze solution.
    A prepared, experienced tech can pull this replacement off (sounds like @hot_rod has done it more than once) BUT I can think of many things that can wrong, good luck!
  • HomerJSmith
    HomerJSmith Member Posts: 1,369
    edited November 2020
    Dave T_2, is correct. If you lose your air charge on the expansion tank, the E-Tank fills with boiler water and when the boiler heats up the expanding water has no where to go because it is already filled with water and not air and the pressure rises.

    The tank looks new. How old is it? If it is an Extrol, the last two digits on the serial number is the year and the preceding two digits are the week.

    I would set the air charge to 15 psi. If you remove the blue cap on the bottom of the tank and depress the valve and water squirts out, you may need a new tank. This tire valve is where you would add air to the air side of the bladder.

    To go from 10 psi, cold, to 28 psi, hot, means your tank isn't regulating.
  • HomerJSmith
    HomerJSmith Member Posts: 1,369
    edited November 2020
    On another post I did give an idea of how to air charge the tank without disconnection it from the sys.
  • MikeL_2
    MikeL_2 Member Posts: 292
    While performing these changeouts, we cover nearby electric components, burner, gas valves, etc. with plastic to prevent accidental drownings.