Hot water heat: zone doesn't run unless another zone is also calling for heat

Discussion in 'HVAC' started by operagost, Nov 9, 2011.

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  1. Nov 9, 2011 #1

    operagost

    operagost

    operagost

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    I have a hydronic baseboard system in which the zone relay built into the aquastat stopped working. Instead of replacing the aquastat, I decided to add another Honeywell R845A and move the thermostat and circulator to that. The new relay is at the end of the "chain" of relays. I am using the provided diagram for a multizone system, which matches the way the existing relays were wired.

    Each zone has its own circulator. The problem zone's circulator is hooked up to terminals 2 and 6. Terminal 2 is also hooked up to the common of the line power. The line hot is connected to terminal 3, which is jumpered over to 5. Terminals 1 and 4 are hooked up to 1 and 4, respectively, from the last relay in the line (which ultimately ends up at ZC and ZP on the aquastat, of course). The thermostat is hooked up to the thermostat terminals.

    When the thermostat in the problem zone calls for heat alone, nothing happens. When another zone calls for heat while the problem zone is also calling for heat, the problem zone starts working as expected. When another zone calls for heat while the problem zone is not, only the other zone runs just as expected.

    I use a Honeywell digital setback thermostat, but I tried changing its batteries and also testing with the old Honeywell round one that it replaced with no change.

    I measured 120V between terminals 2 and 5 (and 2 and 3), but measured 24V across the thermostat terminals only when another zone is calling for heat. When no other zone is calling for heat, there is no power on this relay. So this appears to be the cause of the problem, but I don't know how to fix it.
     
  2. Nov 9, 2011 #2

    Blue Jay

    Blue Jay

    Blue Jay

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    Sounds like your zone control on the problem zone is NOT powered all the time but thru another zone control, you need to have it powered all the time instead of daisy chaned.
     
  3. Nov 10, 2011 #3

    operagost

    operagost

    operagost

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    It's not really "daisy chained"; I have terminal 1 on the previous relay jumped to terminal 1 on this relay. The same is true for terminal 4, so I thought I should have an unbroken link from the ZC and ZR.
     
  4. Nov 11, 2011 #4

    Blue Jay

    Blue Jay

    Blue Jay

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    This is the key to your problem, not passing 24V to thermostat when this zone alone is calling for heat. Need to recheck the wiring.
     
    Last edited: Nov 11, 2011
  5. Nov 11, 2011 #5

    operagost

    operagost

    operagost

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    There appears to have been a break in one of the wires on terminals 1/4, which come from the ZC/ZR on the aquastat. I replaced the wires and all is well. Thanks.
     

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