The Fix-It Playbook — Thermostat Replacement Flowchart | Free 1-Page PDF | 2026 Edition

New thermostat in the box, or the old one going blank? Work the tree before you pull a wire.

Two questions sort it. Is this a standard low-voltage furnace/AC thermostat — line-voltage and heat-pump setups are a different job. Then, breaker off: is a wire already on the C terminal? If yes it's a straight swap; if not, the sheet walks the three C-wire fixes.

The sheet also carries a terminal quick-read (R, C, W, Y, G), and a plain line on when to stop and call a pro.

One page. Print it or keep it on your phone. Free instant PDF download, yours to keep.

If the tree sends you deeper: How to Replace a Thermostat (& Fix the C-Wire) ($6) adds the complete wiring reference sheet, every C-wire workaround side by side, and the troubleshooting table for blank screens, reversed modes and a stuck fan. All five heating and cooling guides come together as the HVAC Maintenance Kit ($14), and all 24 year-round guides are in the Core Library ($49).