Yesterday I had my furnace cleaned per my contract,this morning I woke at 430 and heard the furnace running .downstairs I have a programmable thermostat upstairs is oldfashioned round one still.. when furnace turned off the upstairs thermostat lit up for a split second... I waited till furnace ran again and same thing happened what would cause this is something shorted or is it something I just never noticed... same thermo for 18 years seems odd I never would have noticed.

Does the furnace work is it doing its job? Even after it lights up. A shorted out tstat normally doesn`t work