I live in a 2-story house in AZ and there are 2 Lennox (sic?) heat/AC pumps, one for each floor... it has 2 Honeywell TH8000 thermostats. Last winter there wasn't any problems but tonight it started getting cold so I turned it from cool setting to heat, I can hear relays in the TS click and it says "heat on" but nothing happens, I checked both TS and they both are doing that! I can turn it to the cool setting and turn the TS below the inside temp and the AC will come on okay so the heat pumps/AC units are running (getting power) I turned them off for awhile but no dice!
Right now the inside temp it 71 and I have them both set for 74 and nothing!
Being in the desert there isn't any 'backup' emergency heating all the heating/cooling is performed with the heat pumps only.
Any ideas?

Is the h/p not comeing on at all? Is th blower working in heat mode,if heat pump is running,and blower running,check the copper line the biggest one,, that comes from the heatpump into the airhandler from outside is it hot ?cold? Or what? Check and let us know more detales,the bigger copper line is cold in a/c mode and hot in heat mode.

No the H/P only runs if I put it into cool mode, ditto for the blower (in heat mode if I go to manual fan mode I can turn on the blower but no heat comes out).
Something I noticed is when I turn the upstairs onto heat once the relay closes I can hear what sounds like a small motor (or humming) coming from the attic.. it isn't the blower of course but could it be since I haven't used the heat portion of the system since last April it could be stuck?
It wouldn't seem like both upstairs and downstairs would happen to do that at the same time!
Oh, one more thing.. I had the TS set for heat and went out and manually pushed in the heat pump relay (outside) on one of the units.. don't worry I am careful as I work around high voltage machines in my job.. anyway I held it closed and let it run for a few minutes figuring if it was in heat mode I would feel cool air coming out (as it removed to cold from inside) but it was warm meaning it was removing heat from inside (right?) so it must be stuck in cooling mode...
Oh, thanks very much for responding!