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Can one zone valve receive current from two Stats?

When I replace my current oil boiler with a coal boiler I will need to make at least one of the thermostat controlled zones (zone valves) in my house into a "dump" zone.  An aquastat signal when the boiler hits 210 degrees F. must open a zone valve to dump excess boiler heat.  Can one of my zone valves be linked to both a 24 VAC thermostat (for normal zone heating use) and also a boiler linked aquastat (also 24 VAC) for the purpose of excessive boiler temperature reduction?  What will happen if the thermostat and the aquastat are both energizing the same zone valve at the same time?  Will it work fine in this case, or will it fry the zone valve (and more)?


  • Mike Kusiak_2Mike Kusiak_2 Posts: 604Member
    Should not be a problem

    If you want either the thermostat or the aquastat to open the zone valve, just connect them in parallel. They are basically both normally open switches, so wiring them in parallel presents no problem. If either or both switches close, it will complete the circuit and activate the zone valve. 
  • CoalBoilerGuyCoalBoilerGuy Posts: 15Member
    edited February 2011
    Can one zone valve receive current from two Stats?

    Thanks!  If I'm wiring both the thermostat and the aquastat into a Taco ZCV406 Zone Valve Control Module, will I be wiring them in parallel if I simply connect the switch leads from both the thermostat and the aquastat into the thermostat terminal block for a single zone valve?
  • Mike Kusiak_2Mike Kusiak_2 Posts: 604Member

    Yes, you would connect the wires from both the thermostat and the aquastat to the thermostat terminals. This would be a parallel connection ( two wires to each terminal). Make sure the aquastat has normally open contacts, which close when the setpoint temp is reached. Sometimes referred to as a "reverse acting" aquastat.
  • IronmanIronman Posts: 5,093Member
    Isolation Relay

    If you're feeding from two separate transformers, you may need an isolation relay to prevent the transformers from bucking one another - one of them will loose.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
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