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Explain how Wirsbo actuator works

I have 14 4-wire Wirsbo motorized valve actuators in my radiant heating system. In troubleshooting the wiring and getting ready to expand to more thermostats, I thought it would be a good idea to try to understand how the control works.

1) Both yellow wires carry 24v. I thought a motor would need a ground to work.

2) Aren't the two red wires limit switches that close a ground circuit mechanically when the valve is open to tell the controller to stop supplying voltage to the MVA?


  • Works like......

    1) Yellow wires carry 24 volts and one of the wires is a ground back to the transformer, otherwise it wouldn't work.  The resistance heating melts wax in the actuator, becomes soft and allows the valve to open.

    2) Once the valve opens, it closes an isolated end switch, not to tell the controller to stop supplying voltage because that would close the valve, instead to allow the pump to start pumping and the boiler to start firing.
    Often wrong, never in doubt.
  • LazyDevilLazyDevil Member Posts: 5
    edited November 2011
    I think Ward asked about a Motorized not a Thermal

    The yellow wires drive a 24VAC motor that opens the valve. When power is off a spring closes the valve.

    Just as in the four wire Thermal unit the red wires come from a normally open micro-switch that is closed as the valve opens.

    The Motorized Valve Actuators respond quite quickly. Thermal Actuators respond more slowly with the melting wax.
  • WardCleaverWardCleaver Member Posts: 2
    that's what I thought

    That's how I thought they worked but when I tested the wires I wrote down that I had 24v on both yellow wires. So that didn't make sense.

    The wax units are way cheaper and I would probably replace failed valves with those instead of the motorized ones. I expect I would need to have all wax or all motorized on one thermostat or it would not provide even heat to the areas covered by each valve.

    Thanks for the quick replies.
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