Thermostat messages and settings, explained
What is your thermostat telling you?
Plain answers for the message on your screen or the setting you are unsure about, checked against each manufacturer's own manuals. For US thermostats from Honeywell Home, Google Nest, ecobee, Emerson Sensi, Amazon and Carrier.
- Pages
- 69
- Sources cited
- 173
- Brands
- 6
Look up a message
Find the words or light on your screen. Each row links to a full explanation with the manufacturer's sources.
| On the screen | Seen on | What it means |
|---|---|---|
| "Cool On" flashing | Honeywell Home | The compressor protection delay is running |
| "Wait" | Honeywell Home, Trane | The compressor protection timer is running |
| "Waiting For Equipment" | Honeywell FocusPRO, ElitePRO | The same compressor protection timer |
| "Aux Heat On" or AUX | Heat pump systems | Backup heat is helping the heat pump |
| "Em Heat" | Heat pump systems | Emergency heat: the heat pump is switched off |
| "Recovery" | Honeywell Home | Heating or cooling started early for the schedule |
| "Delayed" or "Starts in" | Google Nest | Google links it mainly to power problems |
| Flashing red light | Google Nest | The battery is very low and charging |
| "No power to Rh wire detected" | Google Nest | A critical power code (E4, E24, E74) |
| "Limit" | Emerson Sensi | Someone set a Temperature Limit |
| "Temporarily Set To" | Emerson Sensi | A temporary hold until the next schedule change |
| "Calibrating" | ecobee | What ecobee documents about the message |
Browse by topic
Delays and waiting
5 pagesBlinking modes, "Wait" and compressor protection.
Heat pumps, AUX and emergency heat
9 pagesBackup heat, defrost and staging.
No heat or no cooling
2 pagesThe thermostat calls but nothing starts.
Cycling and temperature swings
6 pagesShort cycles, long runs and the differential.
Schedules and holds
10 pagesHolds, recovery and learning schedules.
Eco, Away and geofencing
7 pagesWhen the thermostat changes things for you.
Temperature and humidity readings
8 pagesOffsets, sensors and placement.
Modes and fan
6 pagesAuto, Off, fan On, Auto and Circulate.
Power, batteries and screens
7 pagesBlank screens, low batteries and power codes.
Wi-Fi, locks and reminders
9 pagesOffline thermostats, keypad locks, codes and reminders.
Browse by brand
Heating season
- AUX heat vs emergency heat
What is the difference between AUX heat and emergency heat?
- Heat pump vs furnace: which thermostat settings differ
Which thermostat settings are different for a heat pump and a furnace?
- Stage 1 vs stage 2 heat on the display
What does stage 2 heat mean on my thermostat display?
- ecobee AUX heat max outdoor temperature setting
What does the AUX heat max outdoor temperature setting do on an ecobee?
- Nest Heat Pump Balance explained
What does Heat Pump Balance do on a Nest thermostat?
- Why the heat pump or conventional system type setting matters
What does the system type setting on a thermostat do?
How this site works
Manufacturer sources only
Every number and brand behavior comes from a manual or an official support page, listed at the bottom of the page. When a manufacturer does not publish a value, we say so instead of guessing.
Dated and reviewed
Each page shows when it was published and last reviewed, and the date each source was checked.
Stops at the thermostat
We explain what the screen means and what you can change on the thermostat. Anything beyond that is a job for a licensed HVAC technician, and every troubleshooting page says where that line is.