:mad:
On a nordyne-cmf80-pg-di-n lp gas heater what is causing the blower to ignite,then turn back off before the fan system ingages??

Sounds like a bad thermocoupler

Trying to run the furnace at a reduced temperature.

The burner starts, heat exchanger warms up and just before/as the fan starts the burner cuts out. The burner immediately starts the purge/start cycle but by the time the burner starts the heat exchanger has cooled enough to stop the fan so it just does the same thing again.

Does the above sound like your problem?