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blakemw 02-14-2012 04:36 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 07:45 PM

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

Tator1076 02-14-2012 07:48 PM

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

gregzoll 02-14-2012 08:54 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.

BuddyBoy 11-25-2014 03:17 PM

I ran across this thread trying to find the answer to the same question. I was able to answer it myself by a little experimentation. I'm posting to this two year old thread in case anyone else runs across this thread while searching using the same search terms.

The display shows you which components CAN run, and also which ones are RUNNING. Words which are displayed solid show you what is configured, and therefore can run, while words which are flashing also show that the component is running.

So let's say you chose option A or B in the Heat Pump setup (A = fast recovery, B = efficient recover). You would see the words "AUX" and "HEAT PUMP" displayed solid, since those are the components that can run. When the system calls for heat, the word "HEAT PUMP" and the fan icon will begin flashing, showing that those are the components which are running. The flashing only appears for about 30 seconds, after that you need to touch the display to wake it so it shows you the running components. If the requested temp and current temp differ by more than the value programmed into the temperature differential setting, the system will also call for AUX heat, and the word "AUX" will begin flashing as well. In normal operation, you wouldn't expect to see "AUX" flash, but you would expect to see "HEAT PUMP" flash.

If you chose option C in the heat pump setup, you are configuring for no AUX heat. So the word AUX will not appear, since AUX heat is not configured into the system. If you wanted to never use your AUX heating (resistance strips in an all-electric system), you could choose option C. I'm not sure if when you choose option C, you lose your ability to use the heating strips in emergency mode. It may be that you lose the emergency heat feature if you choose option C in the configuration.

I have a 3M-50, not a 3M-30, but I believe they are the same, except the 3M-50 comes with the wifi radio module.

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