I am new to this forum so please let me know if this type of question is not permitted. I have an Aprilaire 8448 thermostat that is set up to control an outdoor wood-burning water boiler as the primary heat and a propane furnace as the aux heat. I cannot figure out the criteria that the thermostat uses to determine when to kick in the aux heat. My HVAC guy over the phone had me hit the mode and temperature up buttons simultaneously to enter a programming mode and had me Change a couple of settings in order to fix this. I noticed today again that the propane kicked on but the house was at 72, the set temperature was 72, and the outdoor boiler was providing 180° water as designed. I don’t understand why the thermostat decided to use propane. Any assistance in figuring out how to change when the auxheat is used would be appreciated. It seems like it uses a combination of temperature and blower runtime????????