Take the two wires going to the thermostat and cross them. If the unit starts, you have a bad thermostat. If it doesn't, at the heater put a jump wire across the terminals where the thermostat wires are connected to. If the unit starts, one of the wires going to the thermostat are broke. If it still doesn't start you may have a bad transformer. Check for 24 volts AC across the two terminals on the gas valve. If yes, bad gas valve. If no, bad transformer.
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Take the two wires going to the thermostat and cross them. If the unit starts, you have a bad thermostat. If it doesn't, at the heater put a jump wire across the terminals where the thermostat wires are connected to. If the unit starts, one of the wires going to the thermostat are broke. If it still doesn't start you may have a bad transformer. Check for 24 volts AC across the two terminals on the gas valve. If yes, bad gas valve. If no, bad transformer.
so simple.thanks for the guidance