Why Does My Heat Pump Keep Switching to Emergency Heat?
When your heating system suddenly flips over to Emergency Heat, it’s completely normal to panic a little. Most homeowners see that alert on their thermostat and think something serious is wrong. Sometimes it is but often, your system is just responding to weather, airflow, or a simple issue that can be fixed quickly.
If you live in Greenville, SC or Birmingham, AL, you’re in an area where heat pumps are extremely common. You also live in a climate where humidity, winter temperature swings, and storms can trigger emergency heat more often than you’d expect.
This guide walks you through why it happens, how to troubleshoot it, and when you should call for help.
What “Emergency Heat” Actually Means
Emergency heat (sometimes called “Aux Heat”) is your backup heating source. It activates when your heat pump can’t keep up or can’t operate safely.
When emergency heat comes on, you may notice:
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Higher energy usage
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Faster warming
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A quiet outdoor unit
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A harder-working indoor air handler
Emergency heat isn’t meant to run all day. It’s a temporary solution while your system figures out what’s going on.
1. Sudden Cold Weather Can Force Your System Into Emergency Heat
Heat pumps work well in mild climates but struggle when temperatures drop into the 20s or high teens. In the Southeast, we get these cold snaps a few times each winter. Often overnight or early in the morning.
Your thermostat notices your heat pump falling behind and switches to emergency heat to keep your home comfortable.
This is normal when:
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A cold front moves in quickly
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The morning temperature dips suddenly
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Wind chills drop sharply
But if your system stays in emergency heat once temperatures rise again, that’s a red flag.
2. Ice or Frost on the Outdoor Unit Can Trigger Emergency Heat
Thanks to winter humidity in both the Upstate South Carolina and Central Alabama areas, frost buildup is common. When the outdoor unit freezes, your system automatically:
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Pauses the heat pump
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Switches to emergency heat
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Activates the defrost cycle
If frost melts and everything returns to normal, you’re fine. If the unit stays frozen, you may have:
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A clogged coil
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A bad sensor
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A malfunctioning reversing valve
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Low refrigerant
These require a technician to diagnose.
3. A Dirty Air Filter Can Force Emergency Heat to Turn On
This one surprises homeowners because it’s so simple.
A clogged filter restricts airflow. When your heat pump can’t breathe, it overheats and switches to emergency heat to protect itself.
If you haven’t changed your filter in the last 30–60 days, start here. This is one of the easiest (and cheapest) fixes.
4. Your Outdoor Unit Isn’t Running — But the Indoor Unit Is
If your heat pump’s indoor unit is working but the outdoor unit is:
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Quiet
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Humming
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Clicking
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Not spinning
…your system will jump straight to emergency heat.
Common causes include:
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A tripped breaker
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A failed capacitor
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A faulty contactor
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Loose wiring
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A bad fan motor
This is where emergency heat is saving your comfort but your electric bill won’t love it.
5. Your Thermostat Is Sending the Wrong Signals
Older or incorrectly configured thermostats can misread temperatures and activate emergency heat without reason.
This is especially common after:
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A thermostat replacement
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DIY wiring
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Switching from a gas furnace to a heat pump
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Battery failure
If your heat pump worked fine until a thermostat change, start your troubleshooting here.
6. Low Refrigerant Makes Your Heat Pump Struggle
Heat pumps don’t “use up” refrigerant. So if the level is low, that means you likely have a leak.
Signs this may be the issue:
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Ice on the copper lines
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Hissing or bubbling noises
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Longer run times
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Room temperatures that never quite reach the set point
When the heat pump can’t pull enough heat from outside, the thermostat flips to emergency heat to help.
7. Your System May Be Undersized for Your Home
If your heat pump isn’t sized correctly for your home’s square footage, layout, or insulation, it’s going to struggle in extreme weather.
This happens often in:
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Renovated homes
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Finished basements
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Bonus rooms
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Add-on rooms
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Older homes with duct issues
When a system runs constantly but can’t catch up, emergency heat kicks in more frequently.
8. Leaky Ductwork Can Make Your Heat Pump Give Up
Both of these regions have plenty of older homes with aging ductwork.
If warm air escapes into the attic, crawl space, or basement, the heat pump has to work twice as hard.
Common signs of duct leakage:
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Hot and cold spots
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Dustier rooms
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High energy bills
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Long run times
Your heat pump switches to emergency heat when duct losses make it impossible to reach the set temperature.
Should You Call for Service?
You should schedule service if:
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Emergency heat stays on for hours
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Your outdoor unit won’t run
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Ice won’t melt off the outdoor coil
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You smell burning or electrical odors
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Your system enters emergency heat when it’s not that cold outside
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Your energy bill suddenly spikes
Emergency heat is a backup, not a long-term heating plan.
Quick Things You Can Check Before Calling
Homeowners can safely check these items:
- Change your air filter
- Make sure your outdoor unit has airflow
- Clear leaves, debris, or ice from around the outdoor unit
- Check breakers in the main panel
- Confirm your thermostat is set to “Heat,” not “Emergency Heat”
- Make sure vents are open and not blocked
If nothing changes after these steps, the issue is likely mechanical.
Emergency Heat Isn’t Always an Emergency
Your heat pump switching to emergency heat doesn’t always mean something is broken. Sometimes it’s doing exactly what it was designed to do.
But if it’s happening repeatedly or during mild weather, that’s your system telling you it needs attention.
Call Air Repair AL if you are experiencing this near you or contact us online with any questions.
Upstate South Carolina – 864-777-1111
Central Alabama – 659-777-1111
Related Information
- Prevent heat pump issues with regular HVAC maintenance.
- Emergency heat often kicks in when your AC can’t keep up — see our AC repair services.
5 Myths Greenville Homeowners Believe About AC vs. Heat Pump