Honeywell Thermostat error codes
13 Honeywell thermostat codes and problems, each with ranked causes, safe homeowner checks and honest repair costs. Count the flashes or read the code on your control board, then find it below. Legends vary by board revision, so confirm against the label inside your unit's door.
| Code | What it means | Severity |
|---|---|---|
| Blank screen / no power | Honeywell thermostat blank or dead with no power? The causes ranked by likelihood, safe DIY fixes you can do today, and what it costs if you call a pro. | DIY-friendly |
| Cool On flashing | Why Cool On flashes on a Honeywell thermostat: compressor protection delay, power resets and short cycling. Easy fixes, $0 DIY to about $350 if a pro is needed. | DIY-friendly |
| Heat not working | Honeywell thermostat calls for heat but nothing happens? Causes like wrong mode, dead batteries, setup errors or a tripped breaker. Costs $0–$1,200+. | DIY-friendly |
| Heat On flashing | Honeywell Heat On flashing usually means a 5-minute compressor protection delay. Learn the causes, safe fixes, and repair costs from $0 to $350. | DIY-friendly |
| Keeps resetting | Honeywell thermostat keeps resetting or rebooting? Common causes are weak batteries, a missing C-wire and power loss. Fixes run $0 to about $500. | DIY-friendly |
| Low battery | Honeywell thermostat low battery warning: causes like weak AA/AAA cells or no C-wire power, how to fix it, and costs from $5 to about $450. | DIY-friendly |
| Not responding to touch | Honeywell thermostat touchscreen not responding? Causes include screen lock, low batteries and frozen firmware. DIY fixes and costs from $0 to about $350. | DIY-friendly |
| Not turning on AC | Honeywell thermostat won't start the AC? Causes like wrong mode, compressor delay, dead batteries or a tripped breaker, plus DIY fixes and repair costs. | DIY-friendly |
| Return to schedule stuck | Honeywell thermostat stuck on hold or won't return to schedule? Causes like permanent hold, app overrides and Smart Response, plus fixes and costs from $0. | DIY-friendly |
| Screen blank | Honeywell thermostat screen goes blank on and off? Covers display sleep, batteries, float switches and C-wire issues, DIY fixes, and costs from $0 to $1,200. | DIY-friendly |
| Wait message | Honeywell thermostat showing Wait? It is usually a 5-minute compressor protection delay. Learn the causes, safe fixes, and repair costs from $0 to $450. | DIY-friendly |
| Wi-Fi not connecting | Honeywell thermostat won't connect to Wi-Fi? Causes like 5 GHz routers, password errors and weak signal, step-by-step fixes, and costs from $0 to $250. | DIY-friendly |
| Wrong temperature reading | Honeywell thermostat showing the wrong temperature? Causes like poor placement, drafts and offset settings, DIY fixes, and costs from $0 to $350. | DIY-friendly |
Don't see your code? Look it up — every search we can't answer goes into the queue for the next guide.