How to Fix a Line-Voltage Thermostat

You don't have to humor a capricious thermostat by walking around wrapped in a blanket. Here's a problem you can likely fix yourself.

Difficulty: Moderately challenging

Instructions

Things You'll Need:

• Neon Or Continuity Tester
• Masking Tape And Pen
• Replacement Thermostat
• Screwdriver

1. 

   Turn off the power to the heater at your main circuit panel. Remove the thermostat cover plate. Remove the mounting screws and carefully pull the thermostat away from the wall or heater, and the wires out of the box (see illustration).

2. Remove one wire nut at a time to test for power with a neon or continuity tester. Probe the grounding wire with one lead and each uncovered set of wires with the other lead. Proceed if the test light does not glow in any test.

3. Identify the house wires that connect to the wires identified on the thermostat as line. Typically they're red. Mark some masking tape with the word line and put it on these house wires. Disconnect all wires to remove the thermostat.

4. Place the thermostat on a table and tape down the wires so you'll have a hand free to rotate the tester knob. Use a continuity tester to test the thermostat. Clip a lead onto a black wire; probe the red wire on the same side of the thermostat while rotating the dial through all the On positions. The tester should remain lighted. Repeat for the other set of red and black wires.

5. Replace the thermostat if it's defective. Reinstall a working one and call a professional to service the heating element.

Tips & Warnings

• Test the tester. Touch the probe of a continuity tester to its tip; it should light if the battery and its own connections are working.
• Never remove a thermostat or any electrical device until you have shut off the power to the circuit.
• Always double-check that power is really off by testing all the wires in an outlet box.