This has been going on sporadically for a couple years and is driving me crazy. It's 50 degrees outside and I have my thermostat set to electric heat at 72 degrees. All goes well until suddenly, the thermostat temp reading drops from 71 degrees to 65. It is NOT 65 degrees in here. That causes the gas furnace to kick in because the demand and actual temp. are 5 degrees apart.
When I turn the system off, the inside temp. still reads 66 degrees which is wrong. I have a free standing thermostat that confirms it actually 71. What is going on? I can find NO temp. pick up sensor in any of the ceiling return vents so I believe the reading is taken at the thermostat. No vents were opened suddenly, nothing!