Hello, I have an Air Pro model #BGM10016B forced air heater with a Honeywell digital t-stat. Yesterday the heat kicked on like normal but wouldn't shut off after reaching the proper temp. I set the t-stat to off but the heater still wouldn't shut off. The heater has a circuit board with an LED but no codes were being displayed. I removed the t-stat from the wall and turned the heater off and it shut down. I turned the heater back on and installed the t-stat and once again the heater kicked on even though the temp was above the desired setting. I changed the battery in the t-stat and all seemed well until this morning when once again the unit would not shut off until I removed the t-stat. Is the problem the t-stat or is the circuit board not obeying the commands? HELP!

If you remove the thermostat only and the furnace goes off it might be the thermostat or a short in the low voltage wiring to the thermostat from the furnace.

Remove thermostat then turn power on to furnace. If the furnace runs it probably has a short in the low volt wiring.

Second test is to hook thermostat back up. Then if the furnace runs past the set point of the thermostat it is possible the thermostat.