I have a reznor f100 natural gas heater. When you turn the thermostat up, you hear a click in the unit and the heater turns on. When you try and shut off the unit by turning down the thermostat, you do not hear that click again and the unit stays on no matter what the room temperature is. I already tested the thermostat (it's fine) and I also made sure that the screws for the thermostat wires are not shorting to keep the unit on.I think it is some sort of defective relay but I don't know where to look for it in order to replace it. Any ideas??
Thanks in advance
Allen