Thermostat calls for heat and turns on fan simultaneously

Heat only system.

The thermostat turns on the fan at the same time it calls for heat.
This causes unheated air to flow until the heat exchanger has warmed up sufficiently.

Kind of annoying if you are near a vent and feel a cool breeze for 20-30 seconds in winter before you get heat.

Any one else experience this?
Or know how to stop it short of unhooking the G wire?
I do use the fan only for air circulation in the summer,

I did test it by taking the thermostat off the wall and connecting R and W together.
Worked like I thought it should.
Burner lit, then after it heated up the fan turned on.

I read where someone else having this issue and they went back through the set up and changed one of the settings. Originally they chose gas heat and then forced air but they said they changed the forced air setting to the other option and that stopped it from happening. Sorry its kinda vague but might be worth checking out

I’ll have to try redoing the setup, but I think if I tell the thermostat I have a system without a fan I will lose the use of running the fan only from the thermostat.


I just found this thread about the same issue and it seems like they are saying it’s the G wire like you mentioned. Maybe someone else will have more input, or ran into this and fixed it another way. Mine is all electric heat pump so I didn’t have the issue.

Re-did the setup and chose gas fuel and then other under type, not forced air.
Tested and ran like it should (waited to heat up before the fan comes on, furnace controlling the fan not the thermostat).
But I lost the ability to control the fan manually.
The option is still there in the app to turn it on but it doesn’t do anything.

I guess I’ll leave it like this for now until summertime.

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I didn’t have this issue but I need have to hit the “flip heat and cool” button from the app. It’s cold outside and the “heat” was blowing cold.

I do not have that button…mine is heat is on when the ac is suppose to be on

Settings >> Advanced >> Swap Heat and Cool

I had the same problem. When I turned on my thermostat the blower would kick in immediately, blowing cold air for a minute. Very annoying. Also, it was using the high speed mode of my blower, which is usually reserved for A/C.

The solution? I simply disconnected the G wire in my thermostat, and the problem is solved. Now the furnace heats up the heat exchanger before the blower turns on (in low-speed mode). Note: I am using a setup with the C wire and no C adapter.

EDIT: Sorry, didn’t see the posts where removing the G wire was discussed. I didn’t know this would remove manual control of the fan.

Same here. Seems like a bug.

If bug hope to see update.

I was experiencing the same issue with Main Blower Fan immediately turning on during the heating cycle.
I found that my Furnace control board has (G) and (GH) terminals. (G) terminals control the main blower fan, not the smaller draft inducer fan. I searched my furnace model found that the (GH) terminal is for heat only systems. Which is what I have.

After connecting to (GH) and testing, the furnace is now operating the same as the old thermostat.
The burner lights first and once the heat exchanger comes to temp the main blower then turns on. Once temp is reached the burner shuts off and the main blower runs until the the heat exchanger cools.

I am no longer getting the immediate blast of cold air when the thermostat triggers a heating cycle.

New firmware update today!
Hopefully this works.
Going to update and test now


Wyze Thermostat Firmware

1.1.2 (March 10, 2021)

  • Changed to a new filter reset mechanism to fix an Android issue preventing filter resets
  • Improved calculations for users traveling across time zones
  • Added a 15 second delay between fan and heating to prevent cold air from blowing before the furnace warms
  • Added a differential temperature feature to give more control of temperature accuracy to balance savings and comfort
  • Bug fixes