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The Honeywell WiFi Smart thermostat was operating fine when on AC until the heat went on this fall. Now, each time the fan goes on, the thermostat loses the connection, turns blank, then reboots itself to the Honeywell screen and returns to normal until the next time the fan goes on and repeats the reboot process.

Here are pics of the furnace and Honeywell WiFi Smart Thermostat Wiring. On the furnace, two blue wires go to the C terminal and one black wire goes to the G terminal while the Honeywell thermostat has the blue wire connected to C and no black wire but a green wire connected to G. There is no black wire. I suspect the G wire on the Honeywell is the problem. What has to be done to get it to operate without rebooting day and night? I tried disconnecting the G wire in the thermostat and the thermostat continued to go blank and reboot each time the fan went on. Any ideas to fix this?

Furnace Wiring Honeywell WiFi Smart Thermostat Wiring Furnace Wiring Overview - Green Wire

  • Do you have multiple zones, and/or multiple thermostats? – Tester101 Nov 18 '14 at 2:41
  • Could you provide a wider shot of the furnace wiring, so we can see what's going on with the green wire(s). – Tester101 Nov 18 '14 at 2:45
  • There is just one zone. Good point. The green wire is shown in this pic attached.!Furnace Wiring Overview - Green Wire – user28070 Nov 18 '14 at 3:29
  • It's strange that there's so many wires connected to that terminal block. Is this an air handler (blows air), or a furnace (heats and blows air)? What other equipment makes up the system (condensing unit, heat pump, secondary heating unit, dampers, zone controller, etc.)? – Tester101 Nov 18 '14 at 13:08
  • The furnace heats and blows air. The only other equipment added years after the furnace installation by another contractor is a humidifier adjacent to the furnace. There is an AC unit outside which ran perfectly with the Honeywell WiFi Smart Thermostat. The blanking out and rebooting of the thermostat began in the fall with the heat on. It is one zone. – Cynthia Nov 18 '14 at 13:47

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