I tested our heating system about three weeks ago and everything was fine including the thermostat. There was no bat lo showing. Tried to turn on the heat today and there is no display on the thermostat. Changed batteries and still no display. How can I fix the problem? Thanks.

I suggest starting by making sure all switches are turned on & the blower compartment door is properly installed. It is possible the thermostat has gone bad. To test, remove the stat from it's base & install a temporary jumper between terminals R & W. If the furnace then fires up, the stat is the problem.