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Low PSI on Columbia MCB 150HD

mfcormier
mfcormier Member Posts: 4
in Radiant Heating

hi, I just drained my radiators to replace my bad expansion tank because I couldn’t get water to my 3rd floor and I still can’t. I notice the PSI is about 12 on the furnace but I pumped my tank to 18. How do I raise the boiler pressure? Thanks for any advice!

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Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,479

    Your prv (pressure reducing valve is factory set at 12psi. Turn the screw in on the PRV clockwise turn it then stop and wait 1/2 turn at a time until you get to 18psi.

    If you measure the height from the boiler to the top of the radiation on the 3rd floor in feet, then take the # you get and divide it x 2.31 the take that new # and add 5 to it that will tell you the psi you need.

    The air pressure in the expansion tank and the prv that feeds the boiler should be set to the same pressure (as close as you can get).

    You have to set the air pressure in the EX tank with no water pressure on the bladder. So it has to be removed from the boiler or isolated from the boiler with a valve and have no water pressure on the bladder when you pump it up.

  • mfcormier
    mfcormier Member Posts: 4

    thanks for your reply. I turned the valve 1 1/2 turns and I got water into my radiators but the pressure reads the same. And the overflow valve let out about a gallon of water into a bucket. Should I back off the screw a half turn?

  • mfcormier
    mfcormier Member Posts: 4

    also, I pumped the extension tank up to about 18psi before installing it.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,479

    Sounds like you have a bad pressure gauge. Replace it. But you can buy a gauge at Supply House.com or some big box store the gauge comes with a garden hose adapter thread and you can install it on the boiler drain valve temporally. Until you get a gauge on there that works you don't know where you are.

    The fact that you increase the pressure, and the gauge did not move makes it suspect.

    You may have too much pressure in the expansion tank so you have no cushion causing the relief valve to open.

    Measure the height and figure out the pressure you need and work from there. With the new gauge you can set the pressure of the expansion tank and the PRV. As I said above you need to remove the ex tank from the boiler to set the pressure.

  • mfcormier
    mfcormier Member Posts: 4

    thanks again. I backed the screw a half turn last night and no water overflowed and the upstairs radiators stayed warm, so I’m good for now. I’m a DIYer so I’ll wait till spring to figure out how to replace the pressure valve and I’ll put a temp on the drain valve for now. Great advice. Thanks again.

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