Questions & answers on how to diagnose and fix backup heat that's not working on a heat pump system.

This article series discusses the diagnosis & repair of backup heat systems used on heat pumps - how to find out if your backup heat is working or partly working, or not working at all.

Backup Heat FAQs for Heat Pump Systems

Trane emergency heat comes on without being switched on.

My Trane emergency heat comes on without being switched on. The auxiliary heat works as normal when it reverses but sometimes it switches to emergency heat by itself, especially on a very cold night. Reversing valve, a switch, ? On 2021-03-30 - by Gale -

- by (mod) - My Trane emergency heat comes on without being switched on.

Gale

It's common for a heat pump system to be set such that backup heat will come on (in response to a call for heat at your indoor thermostat) automagically if an outdoor temperature sensor determines that outdoor temp is so low that the outdoor unit can't keep up with the call for heat.

Only IF that is NOT your case, would I think that this sounds like a problem with

- an outdoor temperature sensor

- a control board or relay in the outdoor unit

Bryant heat pump backup heat not working?

I need a little advice and hope that you can help me. I have a, 8 year old Bryant 213C heat pump & Bryant gas furnace.

This morning (at 35 degrees outdoors) I upped my thermostat from 64 to 69 degrees. The heat pump and furnace fan came on and ran for just a couple of minutes. Then, due to the call for 5 degrees of heat all at once, the Aux gas heat was initiated which makes sense. I heard the gas burner fire up and the vent pipe got hot.

My concern is this: I can hear that my heat pump is still running which of course concerns me as I learned that the 2 units (HP & gas furnace) should never run at the same time. I suppose it could be that the HP is only running in a different mode, such as defrost or possibly in some way that would not be harmful, but it worries. So, I immediately dialed back the thermostat to shut it down.

I don’t know how to confirm if this is a ‘dangerous’ situation or not. I don’t know if the heat pump is supposed to ‘run on’ in some otherwise safe mode temporarily. I am afraid that if I let it run on just to see if it eventually shuts down I might do damage in the meantime.

The fact is that it may have been doing this all along but since I installed a new thermostat I am being hypervigilant now. I am very confident that my thermostat wiring and setup is correct. I would feel better if I knew that the HP is supposed to behave like this under these conditions. Can you comment on this? On 2021-03-23 by Pete -

by (mod) -

@Pete, are we sure that the actual compressor/condenser was running at the heat pump outdoor unit? If so and if the backup heat was on, that'd be unusual and I would TURN OFF the equipment - at least the outdoor heat pump unit - and call your local repair technician for advice and repair. It could be a bad control relay or control board or, of course, something else.

- if you don't have the manual for your unit here is a copy from Bryant - among its "legacy" documents

BRYANT 213C HEAT PUMP OWNERS MANUAL [PDF] (2019) Bryant - 7310 W. Morris Street • Indianapolis, IN 46231, USA, retrieved 2013/03/23 original source: https://www.shareddocs.com/hvac/docs/1009/Public/03/OG-ACR410GEN-03.pdf

by Pete: not sure the heat pump is running

Thank you for your comments and for the link to the documentation! I am not sure if the heat pump is actually running the compressor or doing anything that might be considered 'dangerous' or harmful to the system.

I would doubt that the system would allow for this. It just seems odd that the heat pump would continue making any sound at all once the aux gas furnace has engaged. This is my dilemma.

Where is the backup heat reset button?

Lost power from ice storm 10 days ago. Since then I don't think back up heat for heat pump has been working properly. Is there a rest button? On 2021-02-25 by Carol E -

by (mod) -

@Carol E,

I'm guessing that your backup heat is electric - if not let me know.

Often backup heaters are not working but that problem remains un-discovered until there is in fact a call for back-up heat, so the problem may not itself be storm related.

If I'm right (electric backup) check first that the circuit breakers for that system are not in the tripped position. (Try turning the electric backup heat breaker(s) to the fully OFF position, wait a moment or three, then to the ON position).

If the circuit breakers are NOT tripped off, then

Open the cover to the furnace blower compartment and look for a red RESET button on or near the blower (fan) motor. Try pushing that button in (hear it click and see it stay "down").

Then re-close the blower compartment door, taking care to maker sure that the door is itself fully in position and latched shut.

This care is important because there is often a safety interlock switch on the blower compartment door itself that will keep power to the blower OFF when it thinks the door is open. That's to keep you from getting a finger cut off should the blower fan start while your hands are nearby.

Backup gas heat won't come on in response to thermostat

On a dual fuel Bryant. When thermostat is set at least 5° higher then current indoor temperature. Gas heat doesn't come on. Yet when you put it in test mode the gas heat comes on just fine.

Also noticed no outdoor temp sensor, so no set lockout temp. ( Wondering if that has something to do with it. On 2021-01-27 by Indy

by (mod) -

Indy

Is it the backup heat that won't turn on? If so could be a tripped breaker or safety control.

Check also that the thermostat is wired properly.

Can you test the back up heat on a heat pump system when the outside temperature is 90 degrees ?

Can you test the back up heat on a heat pump system when the outside temperature is 90 degrees ?

I am selling my house and the house inspector said the back up heat doesn't work. It's 90 degrees outside and my HVAC guy said the inspector shouldn't even be trying to run the back up heat. Thoughts ? On 2020-07-17 by Cindy -

by (mod) -

I think your HVAC service technician is correct

 

Heat pump compressor is down, will emergency heat work?

Trying to post a question regarding heat pump.

Heat pump compressor is down, will emergency heat work? On 2020-03-06 by Linda -

by (mod) -

Linda

I can't say if your particular backup heat will work or not, since sometimes a backup system that has not been tested in some time may itself be defective or inoperative.

But in general, properly-installed, the backup heating system for a heat pump system is specifically designed and intended to be capable of providing heat to the building if/when the heat pump cannot operate - such as at very low outdoor temperatures.

Can i remove the gas and the heat pump still work on heat?

I have a house with a dual fuel propane backup heat pump. Can i remove the gas and the heat pump still work on heat? On 2020-03-05 by Keith -

by (mod) -

Keith:

You say the heat pump is dual - fuel. What's the second fuel?

Perhaps you mean it's a heat pump, normally operated by electricity, with backup heat provided by a propane fueled gas furnace / heater.

If that's the case and if you remove the propane then you have no backup heat.

Heat pump can't switch to backup

Have dual heat unit. Came on for one cycle this morning, now nothing. Breaker is ok. Thermostat set at heat, but small print comes up that says aux heat. Nothing happens. Have e-heat for when power is out, but that's not working either. Any suggestions? On 2020-01-21 by J'net -

vby (mod) -

J

It sounds as if your heat pump is telling you that it's trying to switch to backup heat and that your backup heat isn't working.

Is your backup heat electric?

Have you checked the power is on to that system?

Not getting backup heat

I had a new furnace and Guardian heat pump installed over the summer. The a/c worked perfectly during the summer.

I turned on the heat pump and it will run about five minutes, heats great, and then will still run with fan on but no heat. There is a Nest thermostat. The installer doesn't know what is causing the problem.

I would appreciate any suggestions you would have. - anon by private email

MOD Reply:

The good news, Anon, is that the installer is obligated to fix the new system and get it working properly. They can't simply give up.

If I were the tech I'd start by eliminating the thermostat from the equation by removing its wires at the heat pump end, jumping the thermostat heat terminals to call for heat, and see what happens.

Heat pump won't switch to backup heat

Why won't the heat pump switch over to aux heat in really cold weather (<35 degrees)? the heat pump works in warmer weather (>35 degrees), and will keep the house heated to the set temp, but it won't switch over to aux heat (gas heat) in cold weather.

When the weather is really cold (<35 degrees), the thermostat says "aux heat source" (or something like that) when the heat pump can't support the heating needs in the cold weather, as it's trying to use the aux heat source (gas), but the furnace does not kick on with gas heat. (fyi, this is all in "heat" mode)

when i switch the thermostat to em heat (emergency heat), the furnace turns on with gas heat and will heat the house to the necessary temp. On 2018-10-16 by Joe Hangge -

by (mod) -

Joe

When a heat pump won't switch over to aux heating when it should ,I suspect

- a failed temperature sensor outdoors

- a failed control board in the indoor unit or outdoor unit

- the backup heat itself is not working; for example on occasion the service tech will find that electric heaters are burnt-out

Start by confirming that power is on to the backup heating system and if it's gas, that there is gas supply

 

Can I turn off the backup electric heat and just use the heat pump?

Can I turn off the electric coils on my heat pump so only the pump works to heat my house On 2016-03-02 by Anonymous -

by (mod)

If you turn off the backup heat system the heat pump will work to heat your house until outdoor temperature is so low that the heat pump can no longer extract enough heat - then it will try to switch to backup heat and you'll have no heat.

Question: my backup heat is not working on my heat pump

My mitsubishi mr.slim MUH-18RV have heating kit which were not working i bypass the kit and try to stat the compressor seperatly but when i try to start it try to start sounds and become heated , but could not start , before starting the compressor voltage are 212 VAC but when i start compressor voltages downs to 130 volts and all wires become hot . what is the problem is this due to bypass the compressor kit , or its motor is short ? please help me - kalim ullah (July 6, 2014)

On my GE wall mounted heat/ac unit the fan blows but I get no heat or AC. What could be wrong? (Dec 22, 2015) Pete

Reply:

Kalim it sounds like a seized compressor motor.

Pete:

IF you are in a warm climate I suspect your compressor unit is not working. If you are in a cold climate and your heat pump unit is not producing heat it may be that your backup heat (perhaps electric) is not working. Check for a tripped breaker to start.

Question: do I need a backup heat system with my heat pump?

Thinking about purchasing heat pump ..do I need back up (May 28, 2014) Jane
Thinking about purchasing air heat pump is it compulsory to have a back up heat source May 28, 2014) Anonymous

Reply:

The requirement for backup heat for a heat pump system depends on where you live and what cold weather temperatures you can anticipate.

If you are in an area where the outdoor temperatures never fall so low that your particular heat pump system will be unable to heat the home comfortably then yes you need backup heat.

 

Question: Amana heat pump aux light stays on

I have an AMANA package unit that is just out of warranty (of course) and the AUX light comes on (and stays on) even when I lower the heat setting. It is not freezing weather her in Eastern NC and it is kept set to 68-69 degrees.

The unit is not 'iced up'. The 'aux light' stays on even when I lower the setting. What might be the problem? Is it most likely that the 'reversing valve' is stuck? (Dec 26, 2014) Anonymous

Reply:

I'd check first for a failed outdoor temperature sensor.

See HEAT PUMP THERMOSTAT, OUTDOOR

 

Question: Thermostat goes into AUX mode and system blows cold air

Occasionally when heat pump is operating, thermostat goes into "aux" mode and then blows cold air, presently 32 degrees outside temp. Electric heat sequencers replaced. (Jan 7, 2015) tom Geiger said:

Reply:

Still, Tom, if you're not getting warm air out of the supply registers when the aux heat or backup heat is "on" then I suspect it's not really on. There may be a control or wiring problem if the heaters themselves are intact.

 

Question: Aux heat kicks in too soon

I have an electric heat pump for AC and Heating of the home. There is also an auxillary heat that is supposed to come on when temperatures get very frigid. My heat comes on normally with the outdoor compressor activating.

After several minutes the auxiliary heat kicks in even when temps are moderate 30 degrees and above. Thermostat is working correctly, wondering what component in the compressor unit is controlling the activation of the auxiliary heat. Electricity use is way to high this way. (Jan 24, 2015) Anonymous said:

Reply:

Anon

Your HVAC service tech will probably check first the thermostat settings and wiring and then the control board and relays for the heat pump.

See HEAT PUMP THERMOSTAT, OUTDOOR

 

Question: Iced up heat pump; equipment failure at certain temperatures may relate to wiring or controls

Knocked the ice off the top of the electric heat pump's outside unit and now it won't run. We then poured hot water over it to clear away any ice chips - (Feb 17, 2015) Anon

Still won't run. It was operating before we knocked the ice off. What do we do now? We have only aux heat with frigid temps next few days.

When really cold outside 0 degree electric heat wont work. When temp goes up to 10 degrees everything works fine.When 0 degrees and things don't work turn thermostat to emergency heat outside unit shuts down and indoor blower runs but no electric heat. when temp gets to 10 degrees everything normal.

Three service companies checked out this problem and said no problem. (Feb 18, 2015) mike stasko

Reply:

Mike I'm surprised the service companies found no problem since you indicate that the electric heat doesn't work when it's quite cold.

Try hiring an experienced licensed electrician to find the failing control or bad connection.

mike said:
Dan thanks for your response. It just doesn't make sense to me that outside temp would effect emergency heat from the thermostat. looking at wiring diagram from the unit e lug should go right to the air handler in parallel is white wire to outside unit with an optional outdoor thermostat which I'm not sure is in the wiring.

Now with the wire note #3 that wire is removed and could effect w2. What am I missing?

Reply:

Mike

Certainly heat pumps include an outside air temperature that controls the unit's switch to backup heat, right?

 

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