DIY guideThermostat
Replace a thermostat
Check it's low voltage, photograph and label the wires, and swap in a new battery, programmable or smart thermostat. Line voltage is an electrician's.
- 30 min to 1 hr
- 8 steps
- Every step animated
8 steps
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Pull the front off. Thin, coloured wires mean low voltage, and you can carry on.
Thick wires or a line-voltage label (often on electric baseboard heat) mean an electrician.Switch off the furnace's own switch or its breaker, so the wires are dead.
Photograph the wires on their terminals, close enough to read each letter.
Stick the labels from the new thermostat's box on each wire, by its letter.
Undo the wires and unscrew the old plate. Wrap the wires round a pencil so they can't slip into the wall.
Screw the new plate on level, and push each labelled wire into the terminal with the same letter. No C wire for a smart one? Fit its power adapter as its instructions show.
Click the front on, turn the power back on, and run the heat, then the cooling, for a full cycle.
Thick wires, a high-voltage label, or wires that don't match the new one: put the old one back and ask Handyman for an electrician.
What you need
- The new thermostat, with its wire labels
- A small screwdriver
- A drill, if new holes are needed
- Your phone, for photos
- A pencil
Call a pro if
- There are thick wires or a line-voltage label
- The wires don't match the new thermostat
- Heat or cooling won't run after the swap
- A smart thermostat needs a new wire run
Handyman says: Thick wires? I'll find an electrician.
Free for every home. Handyman asks a few questions, then books a pro it trusts.
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