You can fix this
Likely cause: dead batteries
Honeywell lists weak or incorrectly installed batteries first. Fresh batteries brought the screen back, so you're set.
Why this happens
Many thermostats run their screen on batteries even when the system supplies some power. Honeywell's support page lists weak or incorrectly installed batteries as the first cause of a blank screen and recommends fresh alkaline AA or AAA batteries of the same brand. Trane suggests replacing thermostat batteries once a year.
How to fix it
- Check that the time and settings are still correct after the battery swap.
- Set the mode and temperature you want and confirm the system starts.
- If the screen shows Cool On or Heat On and nothing happens, Honeywell suggests waiting 5 minutes.
- Mark your calendar to replace the batteries again in a year, as Trane suggests.
When to stop. If the system still won't heat or cool with the screen back on, use the AC won't turn on troubleshooter.
If this does not fix it, tell the HVAC technician
- That the screen went blank and came back with new batteries.
- How long the last set of batteries lasted.
- The thermostat brand and model.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
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