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A heat pump thermostat prefers to operate the heat pump under "usual" conditions as that is expected to be less expensive. It will invoke the back up (or "emergency heat") when any of several conditions occur: The current indoor temperature is more than 4 °F/2 °C cooler than the temperature setpoint. This is the blockhead approach taken by ...


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According to the schematic, the B terminal does appear to be connected to the transformer. I'd actually trace the wiring in the unit just to confirm, but based on the schematic it looks good. You'll want to make sure the transformer has enough power to supply the additional load of the new thermostat, but typically it isn't a problem. If you hook up ...


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Yes. A bad high limit switch would cause this. The furnace is trying to purge the heat that it thinks is there. Normally the limit switch will reset when the temperature drops. A bad switch will remain open, so the blower will run continuously. This is typically caused by poor air flow through the furnace, which is most often due to infrequent filter ...


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If your power flickered, that might have confused the furnace's electronics. Otherwise, your furnace might possibly have an automatic periodic purge to keep condensate from forming & the burners / blower from rusting. Which make & model furnace do you have? If yours supports periodic purges, that should be mentioned in the owner's manual (available ...



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