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If that happens just jump the low voltage to your wires. Most heat pump setups have two inputs: on/off and heat/cool via the reversing valve.

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You can even wire an old style thermostat in parallel if you want, or have it available to slot in.

Note that this doesn’t always work with smart thermostats. From first hand experience, there are some models out there that will generally work fine but will not complete booting up if one of the outputs is detected as closed.

Yeah, in that case you can get an old thermostat that disconnects easily and wire it somewhere out of the way.

(Though replacing a smart thermostat with a mercury switch one is a five minute job if you're comfortable with it.)

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