Intermittent issue: furnace won't stop heating

[Michaelo]

Installed a 3rd gen Learning Thermostat about 2 months ago:  forced air gas furnace; thermostat wires to Y1, W1, G, C, Rc. 

On three occasions, the furnace will not stop heating.  Thermostat says heating is off, but furnace still going strong.  If I turn the heat up past whatever the current temperature is so that the thermostat turns heating on, leave it for 20 or 30 seconds and then turn it back down, then the furnace will turn off. 

Furnace has been serviced, nothing wrong with it.  Most of the time it works fine, but this issue is frustrating:  last time, I woke up at 3 in the morning, because the house was incredibly hot.  Nest Thermostat says heat is off, but it's not.

Suggestions?  Is it a problem with the base plate?

[zoeuvre]

Hi Michaelo, 

Uh-oh! I'm sorry to hear that your heating won't turn off even though your furnace has been serviced, and it was identified that there's nothing wrong with it. In this case, kindly remove the thermostat display from the base, wait about five minutes, and check if the system turns off or stays on.

Keep us posted. 

Best,

Zoe

[Michaelo]

Removed the thermostat. Furnace turned after after a few minutes 

[zoeuvre]

Hi there, 

Thanks for getting back to us. Follow these: 

1. Shut down the HVAC system at the breaker box. Ensure as closely as possible that all power to the system is off before proceeding.
2. Safely remove any negative wire that is associated with the affected component. In this case, remove the W1 wire. Important: Any removed wire should not touch any other wire, especially a power wire. Instruct the customer to leave the wire(s) sticking straight out and separated from any other wires before restoring power.
3. Leave the thermostat display off the base.
4. Turn the power back on.
5. Wait for a maximum of five minutes to see if the suspected component still turns on and stays on with the display removed.

Let us know how it goes.

Regards,

Zoe

[Michaelo]

The furnace did not turn on

[Michaelo]

Follow up:  it happened again. 
- thermostat set at 19 C

- actual indoor temperature was 21C and furnace had been off most of the day

- mid-afternoon, noticed that the furnace was on

- thermostat still showed it was set at 19C and that the furnace was off 

- turned the thermostat up to 25C, left it there for 15 seconds and then turned it back down to 19 and the furnace turned off

I want some type of fix here.  Do I need to replace the thermostat?

[Michaelo]

It’s been a couple of weeks now, a what’s next?  Other suggestions?  Would appreciate hearing back

[Michaelo]

Hey @zoeuvre can I get an update on what's next?  Is there something else to try, do I return this, is it faulty?