"JohnW" wrote in message
...

As an experiment, I put the face plate back on and pulled up the
thermostat's setup menu where the heating/cooling system is to be selected
and again browsed through the choices (note I've added details for the 7th
item in parenthesis as written in the manual):

1 heating and cooling (conventional)
2 single stage heat pump with no backup or auxilliary heat
3 heat only with no fan (conventional)
4 heat only with fan (conventional)
5 hot water heat only (conventional)
6 Cool only (conventional)
7 multistage heat pumps (heat pump with auxilliary or backup heat)
8 multistage conventional heating and cooling (2 stages heat and 2 stages
cool: requires w/w2 and y/y2 wires)
9 multistage conventional heating and cooling (2 stages of heat and 1
stage cool)
10 multistage conventional heating and cooling (1 stage heat and 2 stages of
cool)

I changed the setting from 1 to 7 and the other heat pump can on
immediately! It cycles off and on periodically as it maintains 70 degrees.
However, now the propane shut off, which always seemed to be running before.

What is the make / model of the furnace to which you have the RTH7400
connected?

Also, do you have the wires connected to the "conventional" or "heat pump"
terminals on the new thermostat?