Honeywell Home thermostat: what its codes, symbols and messages mean
Honeywell Home (made by Resideo) thermostats say most things in words: “Cool On”, “Heat On”, “Wait” or “Waiting for Equipment”. On T6 Pro models a number code appears with an alert icon, and the manual lists what each number means. A blinking “Cool On” is almost always the built-in five-minute delay that protects the compressor.
Words appear in the lower right or under the room temperature, depending on the model; alert codes are read by pressing Menu until the screen shows ALRT. Honeywell Home says each model words the delay differently.
“Cool On” or the snowflake blinking
The thermostat’s built-in delay of up to five minutes. After the compressor turns off, a minimum off timer keeps it off for a few minutes so it does not restart too soon (short cycling), which can damage your equipment.
Honeywell Home thermostats. 2 steps from Honeywell Home on its page. About wiring or power: only Honeywell Home’s own instruction is repeated.
“Heat On” or the flame blinking
Honeywell Home gives the same answer for a blinking “Heat On” or flame as for “Cool On”: the thermostat has a built-in 5-minute delay to protect your equipment.
Honeywell Home programmable thermostats. 1 step from Honeywell Home on its page.
“Wait” or “Waiting for Equipment”
The compressor protection is on: the thermostat is holding the heat pump or air conditioner off for a few minutes so it restarts safely.
Honeywell Home thermostats, including FocusPRO P200 and S200. 2 steps from Honeywell Home on its page.
Blank display
Nothing on the screen: the thermostat has no power from the system or its batteries.
FocusPRO P200 and S200 series. 3 steps from Honeywell Home on its page. About wiring or power: only Honeywell Home’s own instruction is repeated.
Alert code 164: heat pump problem
The L terminal is energized at the equipment: the heat pump is telling the thermostat there is a problem with the heat pump.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
Alert code 170: memory failure
Memory failure in the thermostat.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
Alert code 171: set the date and time
A reminder to set the date and time.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
Alert code 173: internal sensor failure
An alert to replace the thermostat because its internal sensor has failed.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
Alert code 177 or 178: wired sensor reading
An invalid reading from a wired indoor sensor (177) or a wired outdoor sensor (178).
T6 Pro thermostats except the TH6210U. 2 steps from Honeywell Home on its page. About wiring or power: only Honeywell Home’s own instruction is repeated.
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).
T6 Pro thermostats. 1 step from Honeywell Home on its page.
BATT with code 405: low battery
Low battery: replace the AA batteries. The home screen shows BATT, the alert icon and the battery icon, and the backlight is turned off to save battery power.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
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.
T6 Pro thermostats. 1 step from Honeywell Home on its page.
Sources
Honeywell Home’s own help pages only, read on the date shown. Nothing here comes from third-party “codes explained” sites or forums.
- Honeywell Home Support: Why is my thermostat display showing “wait,” “waiting for equipment,” or flashing “cool on”? — Honeywell Home thermostats (each model words the delay differently). www.honeywellhome.com Checked 2026-09-29.
- Honeywell Home Support: Why is the “Cool On,” “Heat On,” “Snowflake,” or “Flame” blinking on the thermostat display? — Honeywell Home programmable thermostats, filed under the Wireless 5-1-1 Day Programmable. www.honeywellhome.com Checked 2026-09-29.
- Honeywell Home (Resideo) documentation: Troubleshooting and Support — FocusPRO P200 & S200 Series Thermostats Installation Manual — FocusPRO P200 and S200 series. docs.honeywellhome.com Checked 2026-09-29.
- 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.