Honeywell thermostat: Alert code 181 or 182: replace filter
A replace-filter reminder: 181 for filter 1, 182 for filter 2. The installer sets each one for fan run time or calendar days (ISU 711 and 712).
Applies to: T6 Pro thermostats. What you see: a code and a symbol and words.
Codes this page covers: 181 182.
What Honeywell Home says to do
- Replace the furnace filter, then dismiss the alert on the thermostat to reset the timer (Menu until ALRT, Select, then + until CLER and Select).
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.