How To Fix It

Aux Heat On but No Heat? Why Auxiliary Heat Isn’t Working

When winter hits and it’s freezing outside, you can find yourself truly grateful for the warmth of your home. But what do you do when the auxiliary heat turns on, yet there’s no heat coming out?

If your thermostat says Aux Heat, but no heat is coming out of your vents, there are a few things to check: clogged filters or venting systems, damaged reverse valves, lack of power, a bad thermostat, low refrigerant, and lack of maintenance. You can fix these yourself, or call an HVAC technician or electrician.

If you’re ready to get up close and personal with your heating system to figure out why your thermostat’s ‘auxiliary heat’ is on, but no heat is being produced, then read on!

We’ll go through a list of problems that can impede your heat from coming, how to fix them, and ways to keep those heating bills from skyrocketing this winter!

Why Is Your Auxiliary Heat On But No Heat Is Being Produced?

For auxiliary heat to turn on, a particular set of events has to happen. You’ll need a working thermostat that is set to a mode other than “off” and a properly installed and maintained HVAC system.

However, even if everything seems to happen as it should, your outdoor unit may encounter problems that may prevent it from turning on.

These include:

Clogged Filter or Venting System

auxiliary heat on but no heat caused by clogged filters

A clogged filter or blocked ventilation may prevent the outside unit from turning on. If the blower has any blockage, it won’t push air through the auxiliary heat exchanger.

This will render the secondary heat exchanger unable to heat up.

How To Fix: Change your filter regularly, at least every month. If the outside unit is not turning on, try removing the blockage by hand.

Read: What You Need To Know About AUXILIARY HEAT?

Have a Question? Ask HVAC Technician

Click here to use the chatbox to speak with one of our technicians.
No in-home service calls. No appointments.

Damaged Reversing Valve

furnace reversing valve

A damaged reversing valve is not likely to provide hot water for your heating system during the winter months.

A faulty reversing valve can cause several issues with your auxiliary heat-including not turning on at all. The reversing valve needs to be working at 100% to provide hot water to your outdoor unit during the winter.

How To Fix: If you suspect damage to the reversing valve, contact a professional for help. They can check out your system and replace it if needed.

Loss of Power

Your auxiliary unit requires a power supply to turn on. If the fuse or breaker flips, your system won’t get electricity to power on its heating element.

How To Fix: If you suspect a loss of power, check to make sure your unit’s breaker or fuse is on. If the breaker tripped due to a system overload, turn it back on and wait for several minutes. If that doesn’t work, contact an electrician.

Bad Thermostat

Econet thermostat

Another possible reason your auxiliary heat isn’t turning on is that the thermostat can’t properly read what’s going on with your heating system.

Temperature sensors inside the HVAC unit determine when the outside unit should turn on. If the sensor is faulty, then your HVAC system won’t know that it needs to activate.

How To Fix: Try turning up the thermostat, ensuring the wires are all attached properly, and screwing it back in if needed. If none of these work, it may be time to replace your thermostat.

If you need a quality thermostat, I recommend this Google Nest Learning Thermostat from Amazon.com. Its features include remote control, Home and Away Assist to reduce power consumption when you’re away, and an Auto-Schedule function to learn your preferred temperature settings at different times of the day and adjust accordingly.

Note: We earn a small commission on purchases, at no additional cost to you.

Here’s a video that explains the steps to follow when replacing your thermostat:

Read: Why Does Home Thermostat Say HEAT ON But There Is No Heat?

Heat Pump Failure

A heat pump that’s damaged and not working is useless. If it can’t provide heating to your home, the auxiliary unit will turn on but won’t do anything.

How To Fix: Call a professional for help. They’ll assess your system and determine if it can be fixed or needs to be replaced.

Low Refrigerant Charge

If your heat pump has a low refrigerant charge, the auxiliary system won’t turn on. This is because there isn’t enough hot water to send through the pipes for heating.

How To Fix: Contact your local HVAC professional to get your system charged back up with refrigerant.

Heat Pump Is Covered in Snow or Ice

Your heat pump is mechanically protected from the outside elements, but it also needs to function properly.

Snow-covered heat pump

When a heat pump is covered in snow and ice, there’s a good chance that it won’t turn on when you activate the auxiliary unit.

How To Fix: If you have excessive snow on your heat pump, clear it off so that it can work properly.

Read: What Causes A Heat Pump To Freeze Up?

Bad Inducer Draft Motor

Like any mechanical system, there are many moving parts in an air handler that need to turn for the system to function.

One critical component is the inducer draft motor. If this starts acting up, your auxiliary unit will fail to produce heat, even if the system has power.

How To Fix: If you suspect that your inducer draft motor is failing, contact a professional for help.

Lack of Maintenance

A lack of regular maintenance on an auxiliary heating system can lead to various problems down the road, so don’t neglect your HVAC system.

How To Fix: Contact your local HVAC company to schedule a tune-up for your auxiliary unit.

HVAC Maintenance Tips

Heat pump service

There are a few small things that you can do to make sure your Auxiliary Unit is up and running when the weather gets cold.

Here are some guidelines to follow to ensure you make the most of your HVAC system:

  • Ensure your filter, condenser, and coils are clean. If they’re not, dust and debris will circulate through the system and clog it.
  • Be mindful of your vents when you’re vacuuming or sweeping around them to avoid damaging them.
  • Keep an eye on your gauge every month to check how much refrigerant is in your unit if you have a heat pump. If it’s low, then add some refrigerant.
  • If possible, keep an eye on the rainout sensors and check for ice buildup when it gets cold out. This is when they’re most likely to freeze up and potentially damage your system.

Tips on Keeping Your Home Warm

You can also take some steps to ensure that your home is warm even when your auxiliary unit isn’t working correctly.

  1. Close your curtains to keep cold air from coming in through your windows.
  2. Ensure you have weather stripping on all exterior doors so that heat doesn’t escape if this is an issue.
  3. Don’t let the filter in your furnace get too dirty since it’ll affect how well your furnace works.
  4. Ensure that any cracks or holes in the floors, walls, and ceiling are sealed up properly so that you don’t have to deal with a loss of heat.

Frequently Asked Questions:

Why Would Auxiliary Heat Come On?

Auxiliary heat will turn on when the weather is cold outside so that you’ll be able to stay warm. This unit provides supplemental heat to make sure your home is nice and cozy during colder months, so it would help to activate it if you need some extra warmth.

Why Is My AUX Heat Blowing Cold Air?

Indoor evaporator unit

If your auxiliary heat is blowing cold air, then there’s a good chance something is wrong with it, and it isn’t working correctly. It’ll need to be serviced to get back up and running, but make sure you also make some HVAC repairs.

How Do You Troubleshoot Auxiliary Heat?

The best way to troubleshoot auxiliary heat is by checking the supply and return air vents. If these are blocked, then this could lead to a lack of heating from your auxiliary unit. You should also check the filters in the furnace and clean them out if they’re dirty.

In addition, if you notice any unusual noises coming from your unit, something isn’t working correctly.

What Does Aux Heat Mean on My Thermostat?

Aux heat on a thermostat means there’s a secondary heating system to provide warmth when the weather outside gets cold. Typically, auxiliary heat turns on automatically when it gets too cold outside for your regular heating to be effective.

Why Is My Heat Pump Not Putting Out Heat?

A heat pump works by transferring warmth from one place to another.

If a heat pump is not producing heat, chances are there’s a problem with the compressor, the reversing valve, power supply, or the unit’s filter. Another possibility is that the venting system is clogged. It could also indicate low refrigerant.

The best way to solve the problem is by contacting a service company that specializes in HVAC systems.

Final Thoughts

If your heat is coming on but not producing heat, then it could be due to a low refrigerant level or the reversing valve. You can also check for other problems like dust buildup or ice blocking the venting system.

Also, don’t forget about the importance of regular HVAC maintenance. Lastly, you might want to schedule an inspection of your unit to make sure nothing else has gone wrong and your HVAC system is functioning correctly.