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I have a Honeywell Thermostat T8131C1012, and a Carrier Heater 58PAV111-16. Between the thermostat and heater there is a normal electrical switch wired in (not sure if that is normal or not...I'ved asked around and noone has heard of a manual switch between the thermostat and heater). I just recently replaced the batteries on the programmable thermostat, but the problem existed prior and still continues. The issue is...the heater will occasionally (1 out of 10 times app.) kick on by itself, but usually I have to go to the basement and flip the manual switch on and off (turning off the thermostat at the unit does not work), and then within a second the heater kicks on and will run until the set temperature on the thermostat is reached. Once the desired temp is reached the unit will kick off correctly, but then it may or may not kick back on even after a 5, 7, or even a 9 degree temp drop. There is no sounds coming from the heater (as if the ignitor was failing or anything else with the heater...once it kicks on it works great). I really think it is in the thermostat, but I want to get some additional insight prior to making any purchases (new home owner and I don't want to start throwing money around already).
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A "normal" furnace has a 24 volt control circuit. It may be integral with the burner control or may be a seperate control transformer. The programmable thermostat has its own power supply, that being the battery. Most hard wired thermostats have a heat anticipator. It is a device that sees a rise and fall in setpoint temperatures and turns on and off the burner. It has a current setting which must match the burner control current rating or else it will "short cycle." If you have access to and know how to use a multimeter, stretch a long single wire from your burner 24 volt common to your thermostat location. Now measure the voltage at the thermostat and the common you ran back to your burner control. The thermostat is just a switching device for the "hot" wire in the control circuit. you should see a constant 24 volt here. this will prove that there isn't a switch in between the burner and the stat.
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