Nest Thermostat loses connection to Furnace

[Daveh3]

Nest Thermostat 3rd Gen

Connected to Electric Forced Air furnace

Problem:

The Nest frequently says it is calling for heat, but the heat does not come on.

It will run like this for 17+ hours, with no heat coming (not very smart for a smart thermostat).

The Next appears to be operating fine, it never turns off or loses Wifi, but it doesn't turn the furnace on successfully.

Resolution:

The only fix I have found is to power cycle the furnace (flipping the breaker on and off in the garage).

This generally works immediately, but it means when I am not home the Nest frequently does not work (and I purchased it so I could monitor and control the heat remotely).

What would cause the Nest to not send the right electrical signal to the furnace, or cause the furnace to reconnect to the Nest somehow after it is power cycled?

[CoolingWizard]

@Daveh3 ,

If as you say, you power cycle, the furnace, and then the furnace starts the heating cycle. You’re describing a problem with your integrated furnace control board ( IFC) and not the Nest Thermostat.  To verify what is actually happening, you’re going to need a multimeter that can measure alternating current (AC) power. 
The next time that the furnace doesn’t start the heating cycle and the nest thermostat says it’s calling for heat, you need to go to the furnace with your multimeter, set the meter to measure AC voltage, put one lead on the W wire, and the second lead on the bate metal frame of the furnace. You should read approximately 24V AC. 

Let me know what voltage you measure. 

AC Cooling Wizard

[Daveh3]

Thank you I will try that.

There were no issues with a regular thermostat prior, but I suppose it is possible the control board has gone bad since then.

[CoolingWizard]

If you do not have a C wire, sometimes we encounter problems like this when the Nest internal battery is low.  Do you have a spare conductor in your thermostat cable or is there only 3 conductors in the cable. 

AC Cooling Wizard 

[Daveh3]

Thank you. There is no c wire unfortunately, I have read about many problems caused by the lack of a c wire.

I have not been able to do the test on the wires to the furnace, but is there a way of seeing if the battery is low?

In the Nest app under Technical Info > Battery it says 3.78 volts

[Daveh3]

@CoolingWizard  Google support chat says "So this will be all resolved David if you install a C wire for your system or the Nest Power Connector to remove the Power Stealing in your current system."

What a terrible product. It clearly said it was compatible with my wiring, I checked it before purchase and knew I did not have a C wire. This is why I purchased the Nest instead of the Honeywell smart thermostat, which requires a C wire. 

Why doesn't the Nest have two AA batteries like a normal thermostat if this is an issue? What an absolute garbage product.

[CoolingWizard]

@Daveh3 ,

on your thermostat cable that’s kind of back in the wall. If you can pull the cable out sometimes they take the spare conductors and they wrap it around the outer insulation cover. If there’s a spare wire, I can coach you on how to hook it up on the inside of your unit and activate the sea wire if there’s a spare conductor wire wrapped around the thermostat cable sheath 

AC Cooling Wizard