Aux Heat Not Kicking In

[Feenix]

My Nest worked great all summer for AC but as Temps dropped I quickly learned that the Aux Heat is not Kicking in at all when needed. I can run the test and force it to work to get the house heated, but the thermostat never turns it on by itself. Instead it turns on the Heat Pump air and blows cold air through the house for hours and hours, losing degrees. 

I had a service tech come check the furnace and the recommendation was to replace the thermostat. Surely there must be a way to resolve this through Nest?

[CoolingWizard]

Feenix, 

Can we double check your thermostat configuration? You say you have a Heat Pump? And your Aux Heat, I assume the Auxiliary Heat, are electric strips in the air handler? 
Go to your Nest Thermostat and check your equipment setup. 
Go to MENU and select, Rotate Ring until you reach EQUIPMENT and select. You should see the back plate and which wires are detected by the Nest. Please respond with list of detected wires.  You should see Rc, Y, O/B, G, C, and AUX.  Your Heat Pump is a “B” model and you need to Energize reversing valve to turn the heat pump into heat mode. 

Ken, The AC Cooling Wizard 

[Feenix]

Detected wires: Y1, G, O/B, Rc, W2 Aux, C

I have the Heat Pump set to O right now in the Pro settings. When I changed that to B and tested it for about 5 minutes it continued to push only cold air.

[CoolingWizard · Accepted solution]

Feenix, 

heat pump systems have a special override control so you cannot switch from Cooling to heating back to back and at forth with out a delay. In order to test heating your system must be off for about 5 to 8 minutes before you switch from Cooling to heating and vice versa.  Turn your system off.  Wait 5 minutes, then turn the heat on and see if the heat pump heats.  You have W2; second stage Heat, and Auxiliary Heat? What are two Heat types ?

Ken, The AC Cooling Wizard 

[Feenix]

Gave the "turn it off and turn it back on again" a try. There is heat!! I am indebted. Now - will this solve it longterm? 

If I'm understanding your question - they are both electrical. I'm not certain of the source of them, as in I don't know which piece of equipment produces the heat. 

(I know how my work boiler works but not my home equipment. Frustrating, but honest.) 

[CoolingWizard]

Feenix,

We can figure this out if you are an adventurous DIY person.  For example your outdoor unit is the compressor, outdoor coil, reversing valve and outdoor fan.  The indoor air handler is the heat pump indoor coil, Blower Fan, Electric Heat strips (Auxiliary/Emergency heat).  
In cooling mode the indoor coil functions as an evaporator coil and the outdoor coil functions as the condenser coil.  When the heat pump switches to the Heating Mode, the indoor coil becomes the Condenser Coil and the outdoor coil becomes the Evaporator coil.  When the outdoor ambient temperature approaches -4°F, the heat pump fails to generate heat. At that time the Auxiliary Heat needs to be activated.  Additionally, those very cold days in the winter, The outdoor coil functioning as an evaporator, will condense water that will turn to ice and the ice will build up on that coil. When that happens the outdoor unit has a defrost controller that activates the defrost cycle,  by reversing the refrigerant flow making it run like an air conditioner. That means the heat goes through the outdoor coil and melts the ice.  At this time, while in defrost cycle the indoor air handler must either a) turn off the blower or b) activate the auxiliary heat leaving the blower on. The goal is to not blow cold air into the house while I defrost cycle.

Depending on which Nest thermostat you have, the auxiliary heat will be landing on the W2 or AUX connector. The control of the Auxiliary Heat is supposed to be managed by the air handler control board. Now, to make this work, the outdoor heat pump must signal the indoor air handler on the W2 terminal when it enters defrost cycle.  Your thermostat cable going outside needs a minimum of 3 conductor wires for that reason. Now, most thermostats will activate the other auxiliary heat all the heat pump system when the setpoint of the temperature exceeds the current room temperature by 5°.  For this reason, if you have your temperature set for say 78°F, and your heat pumps running on a very cold night and cannot keep up, the system will be put into auxiliary or emergency heat by the thermostat and not wait for a defrost cycle.

no overtime a nest learning thermostat will learn about your system and it will learn based on the outdoor environment, indoor environment, and history to understand how well your system works and how long it will take to reach the setpoint that you have asked for. However until it learns this, you cannot expect 100% of its abilities to be available.

Can you check your Nest Thermostat Equipment Configuration please,  Wake up the Nest Thermostat, go to MENU, then rotate the dial to EQUIPMENT, select it, and it will show you a nest backplate and the wires it recognizes. A Green wedge on the connection is GOOD, Yellow is Needing checking. 
Ken, The AC Cooling Wizard

[Feenix]

The connections read green, but only because I found the area in the Pro section to check them and turn them green. If memory serves me well the wedges that were yellow were G, O/B, and W2. Possibly Y1. 

And this is a learning thermostat so this makes much more sense. And I also had it set on Heating/Cooling which I likely won't do again. Turning it off and choosing one or the other for this kind if system seems much more logical. 

[Markjosephp]

Hi folks,

Thanks for sharing your knowledge, Ken.

@Feenix, I hope you've got the answer you're looking for. If you're still in need of any assistance, feel free to let us know.

Best regards,

Mark

[Feenix]

Unfortunately it started acting up again today. And I tried another restart and that did not do the trick. Nest offered to send someone out through Handy and I accepted the offer so maybe that will help. I'm running space heaters and grateful I'm not in a cooler climate. 

[Markjosephp]

Hi there,

Uh oh! I'm sorry to hear the issue still persists.

I'm glad to hear that help is on the way to inspect your system. Please keep us posted, and I would be glad to know what the result would be.

Best regards,

Mark

[EdwardT]

Hi folks,

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,

Edward

[EdwardT]

Hi folks,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward