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Heat only works when fan is manually turned on

Community Member

Hey all - I’m just about at my wits end with this. I just moved into a new home that has three nests, one on each floor. The problem is that there is no air coming through the vents when the heat is on through the Nest, so if the heat is set to 70 and the ambient temperature is 68, the Nest will appear as if it’s heating, but the temperature will continue to drop. The only fix is to set the fan to be on, but then this means the fan always has to be on for the heat to work. Instead, I want the fan to only kick on when the heat needs to kick in, and turn off when the desired temperature is reached. According to the previous owner this is how it worked before I did a factory reset. Does anyone have any idea what could be going on? It’s driving me nuts.


Silver Product Expert
Silver Product Expert

This is just something to look into. I don't know for sure if it will solve your problem...but maybe.

On some Nest thermostats you can configure the thermostat to turn on the fan when it calls for heat. In most situations the furnace (or other HVAC system) will control the fan when the thermostat says it is time to heat. However in rare cases the thermostat needs to call for heat AND tell the system to turn on the fan.  This might explain how a factory reset change behavior. 

For example with a "Nest Thermostat", in the Google Home application, it is at <thermostat name> -> Settings -> Thermostat -> Heat Configuration -> Fan Activation.  I don't know specifically how it is done for Nest Learning Thermostat but hopefully similar. It might be a "PRO" option.

Good luck and hopefully you get heat working again soon!

Thanks for the reply! Unfortunately I’m not seeing that option on my thermostat, I am only able to put the fan back to auto and then I’m in the same situation I was before. Was it possible before the factory reset the Nest was in “PRO” mode and they had this set? Any other ideas?

Community Member

Sorry if this is stupid, but is the wiring correct at the furnace? Could the fan and heat be switched or crossed somewhere?  Trouble shoot- what happens if you do fan only?

Community Member

I had someone take a look today, and they said the cause is that the Nest was only getting around 18V but it requires 24V to kick on the fan automatically. Does this sound right to anyone? I guess I need an HVAC technician now to fix the issue?

I am having the same problem.  Also just moved into home with existing Nest.  Have you had an HVAC technician check and was it a voltage issue?  easy or difficult to resolve?    Thanks so much.  

Community Specialist
Community Specialist

Hey folks,


Thanks for visiting the Google Nest Community. 


Since this thread hasn't had activity in a while, we're going to close it to keep content fresh.

If you have additional questions, feel free to submit another post and provide as many details as possible so that others can lend a hand. 


Hope this helps!


Kind regards,