Hi all,
TL; DR: In my oil fuel forced air system, the thermostat failed to heat the room as it shuts off the forced air fan too early. Issue is temporarily resolved by manually turning on the fan when heating.
Long story begins:
Quite recently our Nest thermostat starts to malfunction when heating the room. The screen shows heat on, but there's no air flow from the vent. When I tune down the set temp below the room temp, the fan starts to blow for about 1 minute before turning off.
Found a few posts in the community with similar issues (post1, post2) and tried all the suggested solutions, including:
- Reset the thermostat and reconfigure the equipment settings.
- Turn off the safety temp
- Fully charge the thermostat with an external charger
- Turn off all the smart settings
- Confirm the wiring setup in PRO settings
- Check the wiring, check the technical info
- I have 2 Nest units at home so I switched to another one
None of them helped.
So I had the hardware checked by a HVAC technician, everything looks good. As is always the case, the system heated well when the technician was here, so I wasn't able to reproduce those weird behaviors in front of him.
After a closer look, I realized that the thermostat is doing its job on the oil burner side: when the heat is on, the oil burner maintains the circulation water temp between 165F and 180F. However, it does not keep the fan running. If I manually keep the fan on, the room keeps getting warm air until the set temp is reached.
For users: if you are having a similar issue and you happen to have a forced air system, I hope this could be helpful.
For Nest engs: this looks like a series bug to me. Please come up with a diagnose and a fix ASAP.
