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Heat Always On

rrabih Member Posts: 38
I had a strange issue these days; the water heating keep running all time even when the thermostat goes above the temperature set in thermostat; the FAN is working well, so no issue with the FAN ; I did luckily noticed this as I sometimes put ON for the FAN to keep the hot air flowing in the house, it saves some energy...

I tried to see if the problem is in thermostat, but even when completely disconnecting the thermostat from the wall, it continues running; I have 2 zones, the zone valve is always on unless I disconnect it manually;
It was working for over 3 years, no recent intervention, I don't suspect any issue wiring;
any clue what this can be? the thermostat is an old Carrier;

thank you


  • Leon82
    Leon82 Member Posts: 684
    Try to disconnect it at the furnace to eliminate a pinched wire running thru the house
    HVACNUT Member Posts: 5,024
    If you turn off the boiler, does the zone valve stay open?

    If the ZV closes, check the wiring for the ZV, at the boiler and the wire to the thermostat for a short. Anyone nail up a picture lately?

    If the ZV stays open, turn off the power to the air handler. Does the ZV stay open?
    If the ZV closes, there's an isolation relay in the air handler that could be faulty.

    If the ZV stays open with both units off, then it's a bad zone valve.

    Does the fan operate in heat mode when the thermostat is set to Auto?
  • rrabih
    rrabih Member Posts: 38
    thank you both, I haven't noticed the issue since it happened for a day, will be able to diagnose the issue better if it does happen again ;
  • Big Ed_4
    Big Ed_4 Member Posts: 2,238
    Seems you have a wiring problem , as mentioned check the thermostat wire ... If you have the thermostat off the wall and the zone valve closes when wire is disconnected , I would check the wire going up to the thermostat .
    I have enough experience to know , that I dont know it all