Why Is My Emergency Heat Running All the Time?
Why Is My Emergency Heat Running All the Time?
If you've noticed your thermostat displaying "emergency heat" or "EM heat" constantly, you're probably wondering what's going on—and worrying about your next electric bill. You're right to be concerned. Emergency heat running all the time is not normal, and it can cost you 2-3 times more than your regular heating system.
Let's figure out why your emergency heat won't turn off and what you can do about it.
What Is Emergency Heat and How Does It Work?
Before we troubleshoot why your emergency heat is running constantly, you need to understand what it actually does.
Emergency heat is your heat pump's backup heating system. When your regular heat pump can't keep up with heating demands, your system switches to this secondary heat source—typically electric resistance heating strips (also called heat strips) or, in some systems, a gas or oil furnace.
Think of it like this: your heat pump is the efficient, everyday heating method. Emergency heat is the expensive backup that should only kick in during extreme situations.
How Heat Pumps Normally Work
Your heat pump works by transferring heat from the outside air into your home. Even when it's cold outside, there's still heat energy in the air that your heat pump can extract and bring indoors.
But here's the catch: as outdoor temperatures drop, your heat pump has to work harder to extract that heat. Below certain temperatures (usually around 25-40°F, depending on your system), your heat pump struggles to keep your home warm on its own.
That's when backup heating should step in—but only temporarily.
Emergency Heat vs. Auxiliary Heat: What's the Difference?
Many homeowners confuse emergency heat with auxiliary heat, but they're not the same thing.
Auxiliary (Aux) Heat: This is supplemental heat that works alongside your heat pump automatically. When outdoor temperatures drop or your heat pump enters a defrost cycle, aux heat kicks in to help maintain your indoor temperature. This is completely normal and temporary—usually running for 10-30 minutes.
Emergency Heat: This is a manual override that bypasses your heat pump entirely. When emergency heat is activated, your system uses only the backup heating source (electric heat strips or furnace). Your heat pump outdoor unit doesn't even run.
If your thermostat says "emergency heat" instead of "aux heat," and you didn't manually switch it on, something is wrong.
Top 6 Reasons Your Emergency Heat Is Running All the Time
1. Someone Manually Activated Emergency Heat Mode
The most common reason emergency heat won't turn off? It was turned on accidentally.
Many thermostats have an emergency heat setting that can be switched on manually. If you have kids, curious visitors, or you accidentally bumped the thermostat while changing batteries, your system might be stuck in emergency heat mode.
What to check: Look at your thermostat display. Most thermostats clearly show "EM HEAT" or "EMERGENCY HEAT" when this mode is active. Check your thermostat settings menu to see if it's been switched to emergency heat mode manually.
Quick fix: Switch your thermostat back to "AUTO" or "HEAT" mode. The emergency heat indicator should disappear within a few minutes.
2. Extremely Cold Outdoor Temperatures
During severe cold snaps—especially when temperatures drop below 25-30°F for extended periods—your heat pump may struggle to extract enough heat from the outdoor air.
If outdoor temperatures have been unusually cold, your system might be relying heavily on backup heat. While this isn't ideal for your electric bill, it's actually your system working as designed in extreme conditions.
What to check: Look at the outdoor temperature. If it's been below freezing for several days, aux or emergency heat running more frequently is expected.
Important distinction: Even in extreme cold, your aux heat should cycle on and off—not run continuously 24/7. If emergency heat is running constantly even in moderate weather (above 40°F), you have a problem.
3. Heat Pump System Malfunction
When your heat pump isn't working properly, your thermostat may default to emergency heat to maintain your indoor temperature.
Common heat pump problems that trigger continuous emergency heat:
- Compressor failure: The compressor is the heart of your heat pump. If it fails, your heat pump can't move heat into your home.
- Refrigerant leak: Low refrigerant levels prevent your heat pump from transferring heat effectively.
- Reversing valve stuck: This valve switches your system between heating and cooling modes. If it's stuck, your heat pump won't heat properly.
- Frozen outdoor unit: Ice buildup on your outdoor unit (beyond normal frost) blocks airflow and prevents heat transfer.
- Faulty sensors: Temperature sensors that aren't reading correctly can confuse your system.
What to check: Go outside and look at your heat pump outdoor unit. If emergency heat is running, your outdoor unit probably isn't running (you won't hear the fan or see it running). If your outdoor unit is covered in ice beyond normal frost, that's a red flag.
When your heat pump is working correctly, you should see both your outdoor unit running AND your indoor heating system operating together. If only emergency heat is running, your heat pump has failed.
4. Large Temperature Differential on Your Thermostat
If you suddenly crank your thermostat up 10 degrees from the current room temperature, your system may activate emergency heat to reach the set point faster.
Modern smart thermostats are designed to do this—they figure your regular heat pump can't bring the temperature up quickly enough, so they engage the backup heat strips to speed things up.
What to check: Did you recently raise your thermostat setting by 5+ degrees? This could trigger emergency heat temporarily.
Prevention tip: Make gradual temperature adjustments (2-3 degrees at a time) to avoid triggering emergency heat unnecessarily.
5. Thermostat Wiring or Configuration Issues
Faulty thermostat wiring or incorrect settings can cause your system to stay stuck in emergency heat mode.
This often happens after:
- A new thermostat installation
- Recent HVAC maintenance or repairs
- Power outages that reset thermostat settings
- Damaged wiring from pests or age
What to check: If you recently installed a new thermostat or had HVAC work done, the wiring might not be configured correctly for your heat pump system.
6. System in Continuous Defrost Cycle
During winter operation, your heat pump's outdoor unit can develop frost on the coils. To remove this frost, your system periodically goes into defrost mode—reversing the refrigerant flow to warm up the outdoor coils.
During defrost cycles, your system can't heat your home, so auxiliary heat kicks in temporarily (usually 5-15 minutes). But if your system is constantly going in and out of defrost mode, your aux heat might seem like it's running all the time.
Causes of excessive defrosting:
- Malfunctioning defrost control board
- Faulty defrost sensor
- Low refrigerant
- Outdoor coil damage
What to check: Watch your outdoor unit over 30-60 minutes. Does it keep going into defrost mode repeatedly? This indicates a system problem requiring professional HVAC repair.
How to Tell If Your Emergency Heat Is Running When It Shouldn't
Here are the warning signs that your emergency heat is running abnormally:
- Your thermostat displays "EM HEAT" or "EMERGENCY HEAT" constantly
- Your outdoor heat pump unit isn't running (no fan noise, no compressor sound)
- Your electric bill suddenly doubles or triples
- The emergency heat has been running for more than 30-60 minutes continuously
- It's not extremely cold outside (above 40°F), but emergency heat is still running
- You hear different sounds from your heating system (electric heat strips make a distinct humming)
If you notice these signs, don't ignore them. Continuous emergency heat operation means either someone activated it manually, or your heat pump has failed.
How Much Does Running Emergency Heat All Day Cost?
Emergency heat is expensive. Really expensive.
Electric resistance heat (heat strips) uses significantly more electricity than your heat pump. While your heat pump might use 2-3 kilowatts of power to heat your home, emergency heat can use 10-15 kilowatts or more.
Cost comparison example:
- Heat pump operation: $2-4 per day
- Emergency heat operation: $8-15+ per day
If your emergency heat runs 24/7 for a week, you could see an extra $50-100+ on your electric bill. Over a month, that's $200-400 in additional heating costs.
This is why fixing the problem quickly is so important—not just for comfort, but for your wallet.
What You Can Check Before Calling an HVAC Technician
Before you pick up the phone to call for professional HVAC repair, try these troubleshooting steps:
Step 1: Check Your Thermostat Setting
Look at your thermostat display. Is it set to "EMERGENCY HEAT" or "EM HEAT"? If so, switch it back to "HEAT" or "AUTO" mode. Wait 10-15 minutes and see if the emergency heat indicator goes away.
Step 2: Check Outdoor Temperature
Is it extremely cold outside (below 25-30°F)? If temperatures are at or near record lows, increased backup heat usage is expected. But remember: even in extreme cold, emergency heat shouldn't run continuously without cycling off.
Step 3: Check Your Outdoor Unit
Go outside and observe your heat pump outdoor unit:
- Is it running? (You should hear the fan and compressor)
- Is it covered in ice beyond normal frost?
- Is there any visible damage or debris blocking airflow?
- Are the fins bent or damaged?
If your outdoor unit isn't running at all while emergency heat is on, your heat pump has failed.
Step 4: Reset Your System
Sometimes a simple reset can fix electronic glitches:
- Turn off your thermostat
- Find your HVAC system's circuit breaker and turn it off
- Wait 3-5 minutes
- Turn the breaker back on
- Turn your thermostat back on
- Set it to HEAT mode and wait 15-20 minutes
If emergency heat immediately comes back on after the reset, you need professional help.
Step 5: Check for Recent Thermostat Changes
Did you recently:
- Install a new thermostat?
- Change thermostat batteries?
- Update thermostat software?
- Experience a power outage?
Any of these events could reset your thermostat settings or cause configuration issues.
When to Call a Professional HVAC Technician
Call a professional for heat pump repair if:
- Emergency heat won't turn off after switching thermostat to HEAT mode
- Your outdoor unit isn't running at all
- Emergency heat is running constantly in moderate weather (above 40°F)
- You see heavy ice buildup on your outdoor unit
- You hear unusual noises (grinding, screeching, banging)
- Your system has been in emergency heat for more than 24 hours
- You've reset the system multiple times with no improvement
- You smell burning or see smoke from vents or equipment
These are signs of serious system problems that require professional diagnosis and repair. Continuing to run on emergency heat not only costs you money—it could potentially damage your heating system further.
Can Emergency Heat Damage Your System If It Runs Too Long?
Emergency heat itself won't damage your HVAC system—after all, it's designed to run when needed. However, running emergency heat continuously for extended periods can:
- Overheat your system: Electric heat strips generate a lot of heat. Running them constantly without proper cycling can cause overheating.
- Shorten equipment lifespan: Heat strips aren't designed for continuous 24/7 operation.
- Mask underlying problems: If emergency heat is running because your heat pump failed, the underlying problem (compressor failure, refrigerant leak, etc.) will continue to worsen.
- Increase fire risk: In rare cases, overheated heat strips or faulty wiring can create fire hazards.
The bigger concern isn't the emergency heat itself—it's WHY it's running constantly. The underlying problem (failed compressor, refrigerant leak, etc.) can cause permanent damage to your system if not addressed.
How to Prevent Emergency Heat Situations
The best way to avoid emergency heat problems? Preventive maintenance.
Regular Maintenance Schedule
Follow these maintenance guidelines:
Every 1-3 months:
- Replace or clean your air filter
- Check your thermostat batteries
Every 6 months (seasonal):
- Clear debris from around outdoor unit
- Check that outdoor unit isn't blocked by snow, leaves, or vegetation
- Inspect visible wiring for damage
Annually (professional maintenance):
- Schedule professional HVAC system inspection
- Check refrigerant levels
- Test defrost cycle operation
- Clean outdoor coils
- Inspect electrical connections
- Lubricate moving parts
- Test thermostat calibration
Regular professional maintenance can catch small problems before they become expensive emergency heat situations.
Smart Thermostat Settings
If you have a programmable or smart thermostat:
- Avoid drastic temperature changes (more than 5 degrees at once)
- Set reasonable winter temperatures (68-70°F when home)
- Use gradual temperature adjustments
- Enable smart features that learn your system's capabilities
Emergency Heat Running All the Time: Quick Summary
If your emergency heat is running constantly, here's what you need to know:
Most likely causes:
- Someone manually switched to emergency heat mode (check your thermostat)
- Your heat pump system has failed (call for repair)
- Extreme cold weather (expected, but should still cycle off periodically)
- Large thermostat temperature adjustment (wait 30-60 minutes)
What to do:
- Check thermostat setting and switch back to HEAT/AUTO mode
- Check outdoor temperature (below 30°F makes backup heat more common)
- Observe your outdoor unit (should be running if heat pump is working)
- Try a system reset (power off for 3-5 minutes)
- Call HVAC professional if problem persists
When to worry:
- Emergency heat runs constantly in moderate weather
- Your outdoor unit isn't running at all
- Your electric bill suddenly skyrockets
- System won't switch out of emergency heat mode
Frequently Asked Questions
How long should emergency heat run before turning off?
Emergency heat should only run for short periods—typically 10-30 minutes at a time in very cold weather (below 30°F). If it's running constantly for hours without cycling off, something is wrong. During moderate weather (above 40°F), emergency heat shouldn't run at all except briefly during heat pump defrost cycles.
Is it bad to run emergency heat overnight?
Running emergency heat overnight isn't inherently dangerous, but it's expensive and indicates a problem. If outdoor temperatures are extremely cold (below 25°F) and your heat pump legitimately can't keep up, temporary emergency heat use is acceptable. However, if you're running emergency heat regularly, you need HVAC system repair—either your heat pump has failed or needs maintenance.
Why is my emergency heat coming on when it's 50 degrees outside?
If emergency heat is activating when it's 50°F outside, you have a problem. At that temperature, your heat pump should handle heating easily without backup heat. Possible causes include: manual activation of emergency heat mode, heat pump compressor failure, refrigerant leak, faulty defrost controls, or thermostat wiring issues. Check your thermostat setting first, then call an HVAC professional.
Can I just turn off emergency heat and use space heaters instead?
Don't turn off emergency heat without fixing the underlying problem. If your heat pump has failed and emergency heat is the only thing keeping your home warm, turning it off leaves you with no heat at all. Space heaters are not a long-term solution—they're expensive to run, less efficient than central heating, and can be fire hazards if overused. Get your heating system repaired instead.
How do I switch from emergency heat back to normal heat?
On most thermostats, you can switch from emergency heat back to normal heat by changing the system mode from "EMERGENCY HEAT" or "EM HEAT" to "HEAT" or "AUTO." The exact steps vary by thermostat model, but typically you press the "MODE" or "SYSTEM" button until you reach "HEAT" mode. Check your thermostat's manual for specific instructions. If the system immediately switches back to emergency heat after you change it, you have a system malfunction requiring professional repair.
Get Your Heating System Back to Normal
Emergency heat running all the time is stressful and expensive, but now you know what to look for and when to get help.
Start with the simple checks: thermostat settings, outdoor temperature, and system reset. If those don't solve the problem, it's time to call a professional HVAC technician. The sooner you address the underlying issue, the sooner you'll stop wasting money on expensive backup heat and get your efficient heat pump running again.
Don't let emergency heat drain your wallet all winter. Take action today to diagnose and fix the problem.