DIAGNOSIS The thermostat is calling for heat (sending power to W1), but the furnace isn't responding. This is usually a furnace control issue or a broken signal chain.
FIX Verify the signal is getting to the furnace.
- On the thermostat, go to Settings > Installation Settings > Test Equipment.
- Run the 'Heat' test. You should hear a quiet click from the wall plate.
- Go to your furnace. With the door panel on (safety switch engaged), you should see a small LED on the control board flash in a pattern when the test runs.
- If no flash, the W1 wire has a break or loose connection at either end.
IF THAT DIDN'T WORK The furnace itself is likely locked out on a safety error (flame sensor, pressure switch). Open the furnace door and count the flashes of the LED on the control board. Look up the flash code in your furnace manual. You'll likely need to clean the flame sensor with fine sandpaper.
HEADS UP The Ecobee's 'Heating' message only means it's sending the signal. It cannot diagnose if your furnace's ignitor, gas valve, or inducer motor have failed. The furnace control board is the real boss.