3rd Gen Thermostat Not Turning On When Temp Drops Below Target

[Mattmci]

3rd Gen Thermostat Not Turning On When Temp Drops Below Target

I have a Nest Learning Thermostat (3rd gen) for a dual fuel Goodman nat gas + heat pump.
The Issue:
When the temperature drops below the target, the thermostat shows that the heat is ‘on’ but the furnace does not actually turn on. Ex, the target temp is set to 68 and the room temp drops from 69F to 66.
However, if I drop the target temp below the room temp and then raise the target temp above the room temp, then the thermostat will say the heat is on *and* the furnace will turn on. Ex, the target temp is 68 but the room temp drops from 69 to 66, if I drop the target temp to 65 and then raise it back to 67, the furnace will turn on.

Our heat is working as we’re able to get warm air through our ducts. Is it a software glitch such that the furnace will only actually turn on when we manually drop the target temp below room temp and then raise it?
The system is less that one year old and has been working fine all winter thus far. The glitch started this weekend.
We are in southeast PA. I have the alt fuel settings set to cut over to nat gas when temps drop below 50F.
I’ve checked to confirm that our software is up to date. Any suggestions on what might be causing the glitch?

[Mattmci · Accepted solution]

Solved:

(facepalm) Always check your filters… I had a hole in my dryer vent that was letting lent escape. I thought surely it couldn’t be the filter causing the issues since it was changed only 5 weeks ago. Nope. It was fully covered in lent. The restricted air flow was causing the furnace to short cycle. 

[GabrielaG]

Hi Mattmci,

Thank you for reaching out to the community. I'm sorry to hear your Nest Learning Thermostat 3rd gen is not turning on when the temperature drops below target, but there's no need to worry. 

• When did the issue start?
• What other strange symptoms have you experienced since the problem started?
• Do you see error codes on the screen of the Nest Thermostat?
• Can you please send me a picture of the Nest Learning Thermostat 3rd gen wiring?

Any additional details you can provide will be helpful.

Regards,

Gabriela

[Mattmci]

The issue was a dirty filter. Once replaced the system worked normally. 

No error messages were shown on the Neat. Is it odd that the Nest did not know the system was short cycling? The Nest continued to assume that the system was generating heat when it was actually turning itself off after one cycle. 

[GabrielaG]

Hi Mattmci,

Thank you for your reply. I appreciate the time you took to respond to this post. I'm glad your system is working normally after you cleaned the air filters. Just to confirm, is the cycling working now on your HVAC system with your Nest Learning Thermostat 3rd gen?.

Let me know how it goes.

Regards,

Gabriela