7 min read • Updated November 2026 • By the CliQ Team — the team that created Blink
How do you replace an old thermostat? Turn off the power, photograph the wires, label each one with the letter of its terminal, swap the old plate for the new one, and connect each labeled wire to the matching letter. You don't need to know what any wire does. You only need to match letters. CliQ is a smart thermostat system that skips most of this: it needs no C-wire, and on select Honeywell Home plates it clicks onto your existing wall plate with no wiring changes at all. $69.99.
Can you replace a thermostat yourself?
Yes, in most homes. The job is easier than it looks because the wires are small and low-power. A low-voltage thermostat is a thermostat that controls your furnace, air conditioner, heat pump or boiler with thin 24-volt wires. Most homes have one.
Check yours in two minutes. Pull the cover off your thermostat. Thin wires, usually two to nine of them, connected to small labeled screws or slots, mean a low-voltage system. Two thick wires, or a plate marked with 120 or 240 volts, mean a line-voltage system, which is a different job (see when to call a pro).
The fear is usually bigger than the work. HomeAdvisor puts professional smart thermostat installation at $200 to $500. A low-voltage swap is a screwdriver job you can do on a weekend morning. It is also worth doing: DOE says turning a thermostat back 7 to 10°F for eight hours a day can save up to about 10% a year on heating and cooling.
How do you replace an old thermostat, step by step?
Do it in this order. Each step is small.
- Turn off the power. Switch off the breaker for your furnace or air handler. Also flip the switch on the furnace if it has one. Low-voltage wires carry little power, but a stray wire touching the wrong terminal can blow a fuse on the control board.
- Take the cover off and photograph the wires. Get a clear shot with the terminal letters visible. A terminal is the screw or slot labeled with a letter, such as R, W, Y, G or C. This photo is your backup.
- Label every wire. Put a sticker on each wire with the letter of the terminal it sits in. CliQ includes terminal and wiring stickers in the box for this.
- Disconnect the wires and unscrew the old plate. Tape the wires to the wall or clip them with a clothespin so they don't slip back into the wall.
- Mount the new plate. Hold it level over the old holes. If the holes don't line up, mark new ones.
- Connect each wire to the matching letter. R goes to R. W goes to W. Match the stickers to the labels on the new thermostat.
- Turn the power back on and test. Run the heat, then the cooling, and make sure the system starts.
You don't have to know what the wires do. Matching letters is enough. The meanings only matter when the new thermostat needs a wire your old one never used.
What if the new thermostat needs a wire you don't have?
This is where "no wiring knowledge" runs out. Many smart thermostats need a C-wire (common wire), the wire that gives a thermostat continuous 24-volt power. Plenty of older homes don't have one. If the C terminal on your old thermostat is empty, read how to check for a C-wire before you buy, and see whether you need one. The WireScanner reads a photo of your wires for you.
Can you replace a thermostat without touching the wires?
Sometimes, yes. CliQ clicks directly onto the existing wall plate of select Honeywell Home thermostats: the RTH111B, RTH221B, RTH2300B and E1 PRO, and horizontal PRO 1000 and PRO 2000 models. No tools. No wiring changes. Click and go.
If your plate isn't on that list, you still have two paths:
- Screwdriver only. If the old screw holes line up with the CliQ wall plate in the box, turn off the breaker, move the labeled wires to the new terminals, and screw the new plate on.
- Standard install. If the holes don't line up, hold the plate level, mark the holes, drill, add the wall anchors from the box, and screw it on. You'll need a drill, a level and a screwdriver.
CliQ needs no C-wire on any of these paths. The always-on Wi-Fi connection lives on a plug-in Hub, so the wall thermostat doesn't need constant power from your wiring. You scan the Hub and the thermostat in the CliQ App, and the install video for your path walks you through the wall. CliQ works with gas furnaces, electric forced air, central AC, heat pumps, and boilers with a standard 2-wire (R + W) thermostat.
When should you call a pro to replace a thermostat?
Most homes don't need one. Call a pro in these cases:
Line-voltage thermostat.
Two thick wires or a 120/240-volt label usually means electric baseboard or wall heaters. This is household current, and CliQ doesn't support it.
Millivolt system.
A gas fireplace or an old standing-pilot wall furnace uses a millivolt system. CliQ doesn't support it.
Damaged or burned wires.
Bare copper, melted insulation or corrosion at the terminals needs a technician before anything new goes on the wall.
No power after the swap.
Check each wire against your photo first. If the system still won't start, a blown control board fuse is the usual cause, and a technician can replace it.
Not sure which side you're on? The CliQ Compatibility Checker answers it in a few steps. For more on whether you need help, see can you install a smart thermostat without an electrician.
No C-wire. Click-in on select plates. Replace your old thermostat for $69.99.
See the CliQ Smart Thermostat →Frequently Asked Questions
Can I replace my old thermostat myself?
Yes, if you have a low-voltage thermostat with thin wires, which most homes do. Turn off the power, photograph and label the wires, swap the plate, and match each wire to the same letter on the new thermostat.
Do I need to turn off the power to replace a thermostat?
Yes. Switch off the breaker for your furnace or air handler before you touch any wires. Low-voltage wires carry little power, but a wire touching the wrong terminal can blow a fuse on the control board.
How do I know which wire goes where when replacing a thermostat?
Photograph the wires first, then label each one with the letter of the terminal it sits in. Connect each wire to the same letter on the new thermostat. You don't need to know what each wire does.
Do I need an electrician to replace a thermostat?
Not for a standard low-voltage thermostat. Line-voltage thermostats, which control electric baseboard heat, and damaged wiring are the cases where a licensed professional is the better call. HomeAdvisor puts professional smart thermostat installation at $200 to $500.
Can I replace my thermostat if I don't have a C-wire?
Yes, if you pick a thermostat that doesn't need one. CliQ doesn't require a C-wire. Many other smart thermostats do, so check before you buy.
Can I replace a thermostat without touching the wires?
On select Honeywell Home plates, yes. CliQ clicks onto the existing wall plate of the RTH111B, RTH221B, RTH2300B and E1 PRO, and horizontal PRO 1000 and PRO 2000 models. No tools and no wiring changes.
Prices verified as of November 2026. Check retailer links for current pricing.
CliQ is independent and not affiliated with or endorsed by the thermostat brands named here. Brand and model names are trademarks of their owners.
Sources
U.S. Department of Energy — Programmable Thermostats — https://www.energy.gov/energysaver/programmable-thermostats
HomeAdvisor — Smart Thermostat Installation Cost — https://www.homeadvisor.com/cost/heating-and-cooling/smart-thermostat-installation/
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