Furnace cycle Question

[blastoff]

I have a Keeprite furnace, new in Oct, 2017 and a Nest wifi thermostat.
Last week or so I noticed/heard the furnace fan cycling when I was outside by the exhaust vent tube, doesn`t go for a long time, havent heard it this week,
So anyone have info if I need to worry, as I would think it should cycle all the time ofr something to be faulty.
On googling it, it says the thermostat is need of changing or furnace fan limit is set ot maual.
I havent had the furnace on since late May,

 

[sirkdev]

?

 

[blastoff]

Thanks, I have the furnace off at the nest thermostat not the power switch at furnace.
I’ll try and turn it on @ the Nest app on phone and see if it runs normal to see if has any codes/flashing lights. I did buy a new Nest today but I may have to call my furnace tech

 

[turbo392]

Nests (Pests) are garbage, especially the newer Google ones and will start glitching their internal relays until your furnace or air-conditioner becomes damaged. Better off with Ecobee or any other smart thermostat

 

[The big greasy]

Ours was doing that. The thermostat sensor was dirty. Took steel wool and cleaned the tip. It runs good now.

 

[Tchetek]

One other note is for the last 20 years or so the electrical code requires the largest exhaust fan in the home be interlocked with the furnace fan. So when the exhaust fan turns on the furnace fan runs also.

lots of times there is a central ventilation switch in a hallway that will also engage both exhaust fan and furnace fan.

They don’t really enforce what exhaust fan gets interlocked, they typically just interlock the main washroom exhaust. (Kitchen hood is probably the largest fan though)

So if somebody was dropping a bomb in the main doucer with the fan on, your furnace fan could be running too.