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Confused - Zone Heats up but no pressure reading on external pressure gauge & no flow

I have a two zone hydronic heating system. I changed out the pump and and purged the lines. On the 1st zone I purged the zone and pressurized they line to 15 psi. On the 2nd zone (upstairs), I opened the drain valve and no water came out. I added water until about the guage on the boiler read 20psi and stopped. I turned on the heat anyway and had the 2nd zone call for heat. All the radiators were heating but when I opened the drain valve water was emptying. After a few days the psi on the boiler dropped to zero again. I can't find any leaks.

Why is there heat in the pipes but I can't detect any pressure using an external gauge or purge the line?


  • Zman
    Zman Member Posts: 7,435

    I am thinking that the boiler drain your are connecting to is plugged.

    As for the leak, have you checked all you radiators for a leaky bleeder? Does the piping go under a slab? Is the T&P valve blowing off?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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