The thermostat is the control device that controls the temperature and sends the power to the burner. If the contacts inside the thermostat fail to connect, the burner will not get power to it.
The thermostat itself is located inside the control box. With the cover off of the control box, the thermostat wiring can be accessed.
The thermostat is the rectangular metal box with the X on it. The two wire connections are at the top.
If a voltmeter is available for testing purposes follow these steps:
- With the thermostat turned to the “OFF” position, there should be 120 V AC checking from one screw to a ground.
- In the “ON” position and high enough to call for heat, there should be 120 V AC on both screws, checking one at a time to a ground.
- If there is 120 V AC on one screw only with the thermostat turned up high enough to call for heat, the thermostat is failing.
- SOMETIMES THIS CAN BE REMEDIED BY TURNING THE KNOB BACK AND FORTH SEVERAL TIMES. IF THE CONTACTS INSIDE THE THERMOSTAT ARE DIRTY, THIS MAY CLEAN THEM.
- If a voltmeter is not available, there is another option for diagnosing a defective thermostat.
- Unplug the power cord to eliminate the risk of electrical shock.
- Loosen one of the screws that connect the thermostat wires to the thermostat and remove one of the wires. Loosen the screw on the other side and add the second wire in with the first. This will have both wires together under the same screw. Tighten the screw.
- Plug the power cord back in and try the burner again. If the burner now comes on, the thermostat is not working and will need to be replaced. While the burner will burn with the wires connected together, there will be no temperature control and the temperature will continue to rise until the hi limit switch turns it off.