Thermostat Cool On or Heat On flashing
About this video
Honeywell thermostat says "cool on" blinking or "heat on" flashing, but not working after changing batteries. Thermostat blinks Cool On or Heat On is a safety time out feature, preventing HVAC compressor from restarting right after stopping. You have to wait for five minutes for pressure inside the system to equalize before the warning message will stop blinking and your AC or a Heat Pump can start again.
Related article summary
This article provides step-by-step troubleshooting for Honeywell Pro Series thermostats, covering blank displays, battery installation, mode setting, resets, lock/unlock, error codes, cooling/heating issues, and model-specific notes for T4/T6. It advises checking power, wiring, filters, and settings, and when to contact Honeywell support or an HVAC technician. Common error codes and user-resolvable codes for smart models are listed, plus helpline numbers and reset procedures.