Douger,

Since it runs fine with the old thermostat, the problem has to be in
the new one. That's the only thing you've changed.

I recently switched to a six-wire, dual fuel (heat pump and gas forced
air) system from a standard three-wire one. The thermostat has a "set-
up" mode that controls a multitude of things (40+) as the system is
rather complicated. It is accessed by pressing a certain combination
of "buttons" on the display and then quickly gets rather cryptic (ie
code numbers and values). But, that should be covered in the manual
and I doubt you would miss it.

The other possibility is that you are getting the wrong kind of
thermostat (hence the six connections). Years ago when I did the same
thing I bought a programmable one that only had three connections.
However, I didn't have a purge motor as it was an 80% job. Maybe my
new system has one, as it is 96% efficient and I just don't realize
it.

Good luck.

dss