Thermostat: add option to disable G wire during heat cycle

I previously had a 4 wire thermostat (Hunter model 44110) and unfortunately only have 4 wires going to the thermostat location, RC, W, G, AND Y with a jumper between RC and RH. Control board has C/X, R/4, W, G and Y. Along with the compressor contactor across C and Y. I did have to install the C-wire adapter and I’m wondering if it has to do with some of this unwanted behavior. I’ve thought about running an extra 18 gauge wire from the control board to the thermostat as a dedicated C-wire, but users in the Wyze forums with a 5 wire setup with a dedicated C wire without the C-wire adapter have run into these issues as well. I’m curious about the operation of the C-wire adapter. Does it contain relays utilizing relay logic? Is it solid state? When in operation the furnace is too loud to hear any clicking of relays. I haven’t had the time to probe it and put together a truth table. I almost want to do a teardown. Anyone have a schematic? The best I could find while searching for C-wire adapter schematics is diode pairs splitting/encoding a single wire into a Y/W, two modes which would normally be operated at different times not simultaneously. Wyze’s C-wire adapter is different in that it sacrifices the G wire turning it into a C wire meaning G operation is combined with another wire. I can see diode pairs combining/splitting Y and W since all they’re doing is energizing relays which are on the most part non-polar. But why the G wire?

  1. Please add option to disable G wire control for heat cycle. My furnace’s fan is controlled by furnace control board and fan limit switch during heat cycle. Confirmed by jumping R to W at the furnace control board with nothing else.
  2. Related to #1. Fan delay on at beginning of heat cycle. Implement short 30-60 second delay before fan on at beginning of heat cycle. Originally controlled by my furnace control board and fan limit switch set to 95°F.
  3. Fan delay off at end of heat cycle too long. Fan shuts off approximately 5 minutes after burner shuts off. Original thermostat utilized heat cycle without G wire. Furnace control board and fan limit switch delayed fan off approximately 30-60 seconds after burner off. However long it took to cool the firebox to below 95F.
  4. When switching thermostat to off DURING heat cycle, both W and G are de-energized bypassing the fan off delay causing the burner to stay lit a short time after the fan turns off. This causes the firebox to overheat and will lead to damage and carbon monoxide leaks.
  5. Add sunrise and sunset settings for schedule and allow for +/- however much time the user would like from sunrise or sunset. Thermostat would have to fetch data from NIST time or weather server
  6. People on the forum have expressed concern about the thermostat being warm to the touch and are worried this may cause erratic temperature readings. I’m thinking it should be fine as long as the RTD or thermocouple is well below the source of heat which seems to be in the area of the display where I’m guessing the main PCBA is located. I noticed there is what appears to be a sensor on the bottom of the thermostat. I think this setup is target as the heat will rise drawing fresh air towards the sensor. Stale air around the thermostat was one of my main complaints about my previous thermostat.

I’ve read on the forum users are disconnecting the G wire at the control board as a work around for the fan timing. I was contemplating doing this, but I need G wire control for my cooling. I can add a jumper between Y and G at the control board to run the fan during a cooling cycle, but I’m not sure if the G terminal will back feed Y through the jumper during a heat cycle causing the compressor to come on at the same time. The best solution for my particular case would be an option to disable G wire control during a heat cycle.

Excellent product so far with tons of potential!

Thanks a bunch!

I think I am in the same boat. I have an older gas unit with no secondary stage. With the old dumb thermostat, I would hear the burner ignite then approximately 10 seconds later the fan would switch on. So far I’ve been struggling with set up as the Instructions in the setup are geared more towards peoe with nice new fancy heatpumps with all the bells and whistles. The fan hasn’t shut off since I set this up and keeps trying to switch to ac. I’m still trying to find the right settings but for now I had to turn off the AC breaker

run a C wire yourself is easier to get Wyze update.

So you are saying to run a separate wire from the control board to the thermostat for the c position instead of using the c-wire adapter?

Check out this thread

Turns out people with 5 wire setups with a dedicated C wire are having the same issues leading me to believe that it’s inherent to the firmware. Unfortunately running a C wire wouldn’t fix it. I should’ve posted this in bugs instead of wishlist.

Most thermostats only enable the g lead when you switch the fan from auto to on. Right now the Wyze thermostat energizes the g lead and the furnace at the same time. This is a bug in my opinion. Standard thermostats just energize the furnace and leave the fan off. This allows the furnace to dictate when to start the fan once the heat exchanger is warmed up. If you have your fan on, a standard thermostat will then shut the fan off while the heat exchanger is warming up, I really hope they fix this soon.


I agree with the OP and the commenters. Furnace manufacturers configure the air-handler fan to operate on a satisfied temperature signal from a sensor in the heat exchanger. The air handler fan is not called to operate by the thermostat (unless the fan operation is selected to “on” instead of “auto.”) This control configuration accomplishes two things — (1) it prevents the room occupants from being exposed to cold airflow during the time it takes the heat exchanger to warm up and (2) it allows for energy recovery from the still-warm heat exchanger by the air handler after the heat source (burner) has shut-off.

I won’t be purchasing a 2nd Wyze Thermostat for my other HVAC unit until this issue is addressed by firmware or a hardware fix.

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Totally agree that whether the thermostat should turn on the fan (G) for heat needs to be a configurable option. I disconnected the G wire to the G terminal and jumped it to the Y terminal for now, so heat & AC works properly, albeit without separate fan control. Agreed that this is more of a bug than a feature.

Same issue.

Old thermostat - heat demand
-sends signal to initiate heat (white wire). The furnace (not thermostat) would then send signal to start fan after about 15-30 seconds after ignition.

  • thermostat did NOT send start signal to fan (green). Fan operation was left to furnace to control.

Old thermostat - fan only demand

  • as expected: when in fan-only mode, thermostat would send signal to fan (green) and NOT to initiate ignition (white).

Wyze thermostat - Heat demand

  • as unexpected: simultaneously sends signal to initiate ignition (white) AND signal to fan (green). I ONLY want ignition (white) and NOT fan (green).

Wyze thermostat - fan demand

  • as expected: when in fan-only mode, thermostat sends signal to fan (green) and NOT to initiate ignition (white).

I would propose that Wyze:

  1. change logic to mimic old thermostat


  1. provide software logic (in heat demand mode) to send only ignition request (white) and NOT fan (green).

Hey Wyze — are you listening???

I’m not happy getting blasted with cold air for 10 seconds at the start of every heating cycle and not happy about putting twice as many starts on my air handler blower as necessary. In the Southern US, we’re running into the season where the A/C needs to occasionally run during the daytime and the heat needs to run occasionally during the evening. I don’t want to have to be running to the furnace twice a day to attach/detach a wire to the fan control, or flip a switch (that I’d need to install and wire.)

Ready to purchase another thermostat for my 2nd zone as soon as this is fixed …

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Haven’t had a firmware update in months. Clearly not a priority for them as they haven’t even given a roadmap

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I submitted a support ticket. They responded and said that they will be putting together a fix for this in about 30 days. They also said that the best way to submit requests like this it to use the wishlist just like we are doing. So hopefully our efforts are fruitful.

Most excellent. I’m looking forward to the update!

As mentioned, thanks to all for supporting the petition for the change.

I received response. I’m not sure it’s what I want but I can at least test when it becomes available

Currently, the fan and heat turn on together anytime heat is called for.
We are however working on adding a 30-second time delay to the fan
so that both the furnace and fan do not turn on at the same time.

That is the response that I received. They don’t seem to understand how this works. Hopefully they will figure it out with the thread.

That’s great to hear you heard back from Wyze. Wish Wyze would just add the option to disable G wire during a heat cycle. My furnace control board handles fan timing just fine on its own. Besides, the G wire turns the fan on high which causes the heater to just blow semi warm air as opposed to when the furnace control board handles the fan which turns it on low speed during heat cycle and actual warm air blows through. I’m sure they studied the behavior of current market thermostats while developing theirs. Wyze, please add the option to disable G wire during heat cycle. Pretty please :pray:

Along the line of not starting the fan until the heat exchanger has heated, I want to be able to disable the Fan Cycle feature. I believe that this feature is similar to older thermostats “Circulate” feature where the fan is turned on without the furnace or compressor starting in order to circulate already conditioned air throughout the house. I have found that this feature works great in A/C mode but in heat mode effectively blowing cold air. I have a duct directly over my bed and with thermostat set to 64 I feel a cold breeze throughout the night from the fan running and the furnace off. The Fan settings should be “Auto”, “On”, “Circ”.

Do you not see those three fan settings, when you swipe up to see “controls” on the thermostat app?

Yes I do - forgot they were there. Thanks.

I am glad that helped!

I am currently dealing with issues related to those fan options. I happened to lose those settings 2 weeks ago… so I miss them and try to figure out how to fix it.(btw I used to have had the fan on AUTO). I have been searching the forum for people with the same issue and I have had no luck.