As soon as i hook up the thermostate it flashes the 3 flashes code and i have already tryed a new thermostate .... as soon as i unhook the thermostate it flashes for normal operation with no call for heat it is a 75000 natural gas
Heating & Cooling - Mr. Heater - Natural Gas Garage Heater - 45,000 BTU
Answers & Comments
3 flashes is a pressure switch code. Either you have a bad/plugged up pressure switch, cut pressure line leading from the flue box, or a plugged tap that the pressure line attaches to which feeds the positive pressure to the pressure switch.
Try using it without the thermostat, tie the two thermostat wires together or put a jumper between
r and w. If furnace operates, you must have wrong style of thermostat