Another thermostat Question.
I have the old mercury thermostat and recently had an issue with my propane HVAC. I had the furnace repaired. I've recently noticed my system has a cycle of staying off longer every so often. I first notice the other day when i thought things seemed a bit chilly. I looked, and the temperature was below the usual by a few degrees; however, it kicked on shortly thereafter. It runs normal cycles for a while afterwards. I would estimate 2 of these longer cycles in a days time. What could be causing this?