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blakemw 02-14-2012 03:36 PM

3M-30 Thermostat AUX HEAT PUMP on display
Installed the 3M-30 and the display shows AUX HEAT PUMP instead of just HEAT PUMP. Rechecked wiring and install instructions several times. When I change the programming only the HEAT PUMP flashes, AUX. Is this think running on HEAT PUMP or AUX HEAT PUMP?

hvactech126 02-14-2012 06:45 PM

call the manufacturer of the stat.....................

Tator1076 02-14-2012 06:48 PM

Aux means heat pump is on. Best way is to walk outside and see if its on.

gregzoll 02-14-2012 07:54 PM

Don't you mean the 3m-50, or ct-30? Aux heat would be your furnace inside. BTW, how cold is it outside, and have you made sure that the mode is set properly? If you do not want Aux heat, set the mode for C, otherwise set for A. Then check your Swing & Differential settings after pressing Menu, when you have the thermostat set for Heat or Cool.

More info can be found at

This from explains how the thermostat uses Aux heat:

Unless the old thermostat had an external temperature sensor, it would not know when to use aux heat.

The heat pump tries to maintain the room temperature. The 3M50 turns on aux heat when the room temperature is below the set DIFFerential (default 2F). So if the room temperature droops below 2F, the aux heat comes on with the heat pump also on all the way to target (fast recovery). And if there is a set back over the DIFF, the same thing happens for recovery. The objective is to minimize the use of aux heat until it is needed.

To test the aux heat, go to the temporary screen, turn on the EMER (touch), the pump will be off and only the aux will be used.

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