Aux Heat Showing on Thermostat but not Producing Heat

[Cuffdunk]

Aux heating was required overnight for the first time this year. This morning, my thermostat was showing Aux Heat, but I wasn’t getting any. It’s clearly noticeable because my upstairs and downstairs are on totally separate, identical systems, both were on aux Heat, and the upstairs is producing much warmer air.

Electric heat pump forced air system

troubleshooting steps tried:

the two thermostats were wired identically, but I reran setup downstairs and moved the RC wire to the RH slot which is where setup told me to put it this time. (Don’t think this really matters. Nest sees it as the power wire)

Reseated the w2 aux wire 

full reset to factory settings on the thermostat

What can I do? Will attach pics of current wiring and the old Honeywell.

(edit: I don't see an option to add a photo anywhere - no camera icon, which I've seen suggested elsewhere. How do I do that?)

[OlegN]

the same story.  I see more posts about it in last day. I guess it just happened, there is some bug in nest software...

[CoolingWizard]

@Cuffdunk , please allow me to explain a bit about he typical heat pump operation when using a thermostat that is heat pump system smart.  When a heat pump is installed, and based on where geographically it is located, the indoor unit should have electric heat strips installed in it. This electric heat strip(s) is the auxiliary heat and the Emergency Heat. The auxiliary heat is controlled automatically by the thermostat and the outdoor heat pump unit. Inside the outdoor heat pump unit there is a Defrost Control board (DFC). When the outdoor unit is in heating mode ice will build up on the outdoor coil over time. When the ice reaches a point that it is detected by the DFC frost sensor, the DFC takes control of the Heat Pump, reverses the refrigerant flow, signals the indoor unit to energize the heat strips, slow the blower speed down to low and this cause the system to take heat from the inside to use it to melt the ice.  Basically, it turns into an air conditioner briefly.  Once the ice is melted, the DFC resets the system back to Heating mode, and releases control back to the main control board. When the thermostat detects that the heat pump is not keeping up with the infiltration of the cold air, the thermostat will turn on the auxiliary heat to boost the heat production.  

The function of Emergency Heat is that the unlike the Auxiliary Heat control, the homeowner is the controlling point. The thinking is that if the heat pump fails, the homeowner can turn the unit OFF, then turn the Emergency Heat On and get heat in the house while they wait for the repair company to arrive and fix the heat pump. 

For your specific problem, you need to check the indoor unit to ensure the Circuit Breaker is not tripped.  The heat strips typically have their own separate circuit breaker.  If the circuit breaker is not tripped, then perhaps the Heat Strips themselves have a failure.  In this case it is time for an HVAC technician to make a service call on your home.  

AC Cooling Wizard

[Cuffdunk]

Circuit breaker is not tripped, and Aux Heat worked fine when I swapped my old honeywell back in place of the nest temporarily this morning. Much "hotter" heat coming out of the vents, room heat immediately coming up, etc.

[OlegN]

See my last comment. My issue was that heat pump in control board in the air handler was not set up correctly. May be it is your issue too.

[CoolingWizard]

@Cuffdunk  Post a picture of your Nest Thermostat wiring and a picture if your old thermostat and its wiring. 

AC Cooling Wizard

[OlegN]

the same story.  I see more posts about it in last day. I guess it just happened, there is some bug in nest software...

all worked fine  until two days ago.  next step is to replace  nest ... but looks like it some software glitch. or may be it is broke long before, but we noticed it only now when temperature outside  fell form 50-60- to 21

[CoolingWizard]

@OlegN , The Nest Learning Thermostat has a default of 25 degrees as the point where the typical Heat Pump begins to loose efficiency. As it monitors the system performance it will determine if Auxiliary heat is required.  When it activates the Auxiliary Heat it does this as a heat booster for the heat pump.  The key for all of this to work is to ensure the air handler has a variable speed blower, and a heat pump aware control board. 

AC Cooling Wizard

[OlegN]

Thank you for your explanation. Here is the story again: Auxiliary heat is on showing on the thermostat. But no signal is sent to turn on the heating coil.  If I switch thermostat in Equipment/Test Aux heat ,ode  it turns on heating coil. May be my AUX heat never turned on with this thermostat? I just notice it when  it was lower then 25 degrease outside.

I have goodman AVPTC49D14BB AIR HANLDER  and GSZ160421BE heat pump.  will it work with nest?

[CoolingWizard]

@OlegN , well congratulations you have a very smart indoor air handler in your Goodman AVPTC49D14BB, and it’s paired to an outdoor unit, the GSZ160421BE unfortunately is not a smart talking unit. The indoor air handler has both a conventional, and an advanced 2-wire digital communications interface.  The electric heat strips are not factory installed and if needed, they must be installed in the field by the HVAC contractor.

There are very complicated performance parameters that must be set up by the installing contractor using a Bluetooth app.

AC Cooling Wizard

[OlegN]

as I mentioned, I have  electric heat strips installed.  

[OlegN]

and we do adjust parameters via Bluetooth. and heating strips do work when I do test aux heat form NEST.  but when AUX heat is on in normal mode,  it is not  sending signal to activate heating strips.

[OlegN]

I resolved the issue.  When you pointed out that my heat pump is not communicating type, I checked wiring on the control board, and so that  there is no communication to heat pump wires connected.  I connected to the control board of the  air handler via Bluetooth app coolcloud and set up NON COMM heat pump, single stage ( for my unit type).  AUX heat started turning on from nest right away in all modes. So it works now.  I guess it ha snot been working ever,  as it was showing that aux heat is on, but it was not. We really noticed it when weather got below 25 degrees F. One remark, I had to also set up tonnage for the heat pump in the control board, so fan is not blowing to much air and not making to much noise in the house.

[Cjacobs129]

Are you saying that the Nest bypass the outside unit at 25 degrees and then run exclusively on heat strips sending no W call signal to the outside unit?

[OlegN]

I was saying that since  we installed  this new ac heat pump system, AUX heat was never really on. House was heating form the heat pump as outside temperatures were not that  low.  and we used fireplace and heaters...  But this season I noticed that house was not heating even nest showing AUX heat.  nest was turning heating coils when I tried test mode.  

I was already ready to change thermostat, then started  playing with airhanlder control board.  When I set up outside unit type correctly: non comm single stage heat pump, it started turning on AUX heat...

[Cjacobs129]

My real question is, does the Nest thermostat, at some temperature, say 35 degrees, calling it auxiliary heat and completely bypass the outside unit and only run on the heat strips. My new house a new smart thermostat that is doing this and I don’t want to replace it with another one that does. 

[CoolingWizard]

@Cjacobs129 , this depends pn how your HVAC system is set up. For example, of your system has electric heat strips and wired with an W2/AUX wire, the Nest will only activate the auxiliary heat strips when the heat pump is running for long period and the temperature continues to drop.  It does this to “boost” the heat output. 

If the house is drafty, there will be an increase of cold air penetration onto the home. This will cause the heat pump to work harder. Most heat pumps can produce heat effectively down to 20 degrees before heating capacity drops. Also, when the heat pump coils ice up, the Defrost Control Board takes over and activates the auxiliary heat while it defrosts the ice. 

AC Cooling Wizard

[CoolingWizard]

@OlegN, the contractor that installed your heat pump snd indoor air handler clearly did not set up the system correctly. Since the indoor unit was expecting communications it could not activate advanced features. As a result the auxiliary heat system was not active. 
Be careful using the CoolCloud app since it can used to change many features of your air handler which in turn can damage the equipment. 
Also, it is very interesting that they installed a high end air handler with a generic outdoor heat pump unit.

AC Cooling Wizard 

[OlegN]

Thank you for your  input. Yes, I realized it too eventually. I was purchasing the system online. It was Aug 2020.. Everything was  on backorder.  It was packaged together on that website.  https://www.acwholesalers.com/Goodman-GSZ160421-AVPTC49D14/p87491.html

1 x	(Kit) Goodman 3.5 Ton 16 SEER Heat Pump Variable Speed Air Conditioner (GSZ160421 AVPTC49D14)   - (1) Goodman AVPTC - 3.5 Ton - Air Handler - Multi-Position - Variable Speed ECM Blower (AVPTC49D14)   - (1) Goodman GSZ16 - 3.5 Ton - Heat Pump - 16 Nominal SEER - Single-Stage - R-410A Refrigerant (GSZ160421...    Lift Gate Service Yes, I'll Need A Lift Gate	$3,019.86
1 x	Goodman 10 Kilowatt 34,100 BTU Heater Coil for Smart Frame Air Handler (HKSC10XC)	$85.74

I am wondering why did they package them like that. Anyway, Installer tested heating kit in test mode so they did not know about bluetooth software to control airhandler:(    Now I think am comfortable to use cool cloud.  Adjusted tonnage for the heat pump, so make noise from airflow comfortable. Well at least It heats house now, no problem.