Honeywell thermostat: Only BATT on the screen, code 407: critically low battery
Critically low battery: only BATT, the alert icon and the battery icon are shown. Replace the AA batteries.
Applies to: T6 Pro thermostats. What you see: a code and a symbol and words.
What Honeywell Home says to do
- Replace the AA batteries.
Source
Honeywell Home’s own help page, read on the date shown.
- Honeywell Home (Resideo) documentation: 7. Alerts and Reminders — T6 Pro Installation Manual — T6 Pro thermostats (codes 177 and 178 not on the TH6210U). docs.honeywellhome.com Checked 2026-09-29.
A similar symbol on other thermostats
The same symbol on another maker’s thermostat can mean something else.