If your heat pump happens to freeze during winter, don’t panic because you’re not alone. A layer of ice on your outdoor unit is rather normal during cold weather. However, if the whole unit looks like an ice block or stays frozen for hours, something is wrong.
In this detailed guide, you’ll learn why your heat pump freezes up, what to do if this happens, how to safely defrost it, and how to prevent the problem from returning.
Is It Normal for a Heat Pump to Freeze in Winter?
Yes — to a certain extent. During cold weather, moisture in the air condenses and freezes on your heat pump’s outdoor coils as it extracts heat.
All units have an automatic defrost cycle that melts that frost for you, so some frost or light icing on the coil is normal and usually temporary.
However, it is not normal for a heat pump to completely freeze and refuse to defrost. This is indicative of a problem that is preventing the natural defrost cycle from occurring or proper airflow. If this is allowed to continue, it could mean compressor damage, system failure, or highly expensive utility bills.
How the Defrost Cycle Works
Understanding the defrost cycle helps you recognize when something isn’t working right.
1. Periodically, the heat pump checks coil temperature and time of operation.
2. In case of frost buildup, it temporarily switches into cooling mode: hot refrigerant passes through the outdoor coil to melt ice.
3. The outside fan typically stops operation to aid the coils in warming up quicker.
4. When the sensors detect that ice has melted, the system switches back to heating mode.
A normal defrost cycle lasts about 5–15 minutes and is done automatically a few times per hour during cold weather.
Well, if your heat pump remains encased in ice for hours, the defrost cycle has likely failed — and it needs attention.
Also read: Heat Pump Not Heating
Why Your Heat Pump Freezes Up in Winter
Here are the most common reasons your heat pump is frozen in winter, what each means, and how to fix it.
1. Blocked Airflow
Symptoms: These may include heavy icing of the coil or fan blades, reduced heating performance, or non-free-spin outdoor fan.
Causes:
•Dirty air filters
• Blocked return vents or registers
• Debris, snow, or leaves clogging the outdoor unit
Why It Matters:
Poor airflow restricts the heat pump from pulling in enough outdoor air and causes moisture to freeze on the coil faster than the system can melt it.
Solution:
• Replace or clean air filters monthly.
• Remove snow, ice, or leaves around the outdoor unit, allowing at least 2–3 feet of clearance.
• If necessary, gently hose off debris from the coil.
2. Faulty Defrost Control Board or Sensor
Symptoms: Unit remains frozen solid, never goes into or out of defrost mode, or does erratic cycling.
Cause:
It is controlled by the defrost control board, which dictates when the system is supposed to go into a defrost. If there is a failure of this board or a faulty temperature sensor, then the defrost cycle might not kick in properly.
Correcting:
• Reset the system at the breaker to see if it resumes normal operation.
•If it still refuses to defrost, call a qualified HVAC technician who can test sensors, relays, and the defrost board for any issues.
3. Low Refrigerant Levels
Symptoms: Reduced heating output, ice forming along the refrigerant lines, or gurgling noises.
Cause:
Low refrigerant—often caused by leakage—lowers the temperature of the coil and makes moisture freeze rapidly.
Why It Matters:
Operating with low refrigerant damages the compressor, which is the most expensive part of your heat pump.
Solution:
Only a licensed HVAC professional should handle refrigerant. They’ll detect and fix leaks, recharge the system, and check pressures.
Also read: Furnace Not Staying Lit
4. Fan Outdoor Issues
Symptoms: The fan is either not operational or spinning very slowly; this leads to uneven frost accumulation.
Cause:
A defective fan motor, capacitor, or jammed debris will impede the fan’s action of moving air across the coil. Without airflow, ice builds up rapidly.
Correctness:
•Shut off the unit immediately.
• Clear debris or ice from fan blades.
• If it won’t still start, then let a technician inspect and replace either a motor or capacitor.
5. A malfunctioning thermostat or reversing valve
Symptoms: The heat pump either does not switch into defrost mode or remains in heating mode.
Cause:
The refrigerant flow is routed by the reversing valve between heating and cooling cycles. If the valve sticks or the wrong signals are issued by the thermostat, it may not defrost.
Correct:
An HVAC technician will test the wiring of the thermostat, reversing valve coil, and refrigerant pressures.
6. Poor Drainage or Improper Installation
Symptoms: Ice at the bottom of the unit, water pooling around it.
Cause:
When melted ice can’t drain away it refreezes around the base of the coil. Inadequate drainage or improper unit levelling causes this.
Fix:
• Make sure the heat pump sits on a slightly elevated base.
•Snow and ice around the base must be removed to provide proper water runoff.
7. Extremely Cold Weather
Even the best heat pump has problems operating in temperatures below freezing. Below 20°F (-6°C), moisture freezes out of the air faster than the defrost cycle can remove it.
Correcting:
• Use auxiliary or emergency heat during extremely cold spells.
• Avoid manually switching to the defrost mode unless instructed to do so by a professional.
• Consider cold-climate or dual-fuel heat pumps if you live in very cold regions.
Also read: Furnace Short Cycling
How to Defrost a Frozen Heat Pump Safely
If your heat pump is frozen over, follow these safe defrosting steps:
1.Shut off the system at the thermostat.
2. Switch to “Fan Only” mode: This will help circulate warmer indoor air through the system.
3. Clear snow/debris from around the outdoor unit.
4. Do not chip or scrape the ice because this can damage the coils and fins.
5.Gently melt ice formation by spraying a garden hose in warm, not hot, water.
6. When thawed, return to normal heating mode and observe operation.
If it freezes again within hours, that’s a sure indication you have some sort of mechanical or control problem and should schedule a professional inspection.
Also read: Heat Pump Not Defrosting
What NOT to Do When Your Heat Pump Freezes
• Don’t pour boiling water on the coils; it will lead to metal shock and cracking.
•Don’t hit or scrape the ice with sharp tools. The fins are delicate.
• Don’t ignore the problem – running a frozen heat pump can ruin the compressor.
•Don’t disable the defrost cycle or disconnect sensors.
How to Prevent Your Heat Pump from Freezing during Winter
Proper maintenance and a few smart habits can help you avoid most freezing problems.
1. Keep Air Filters Clean
Dirty filters restrict airflow, which leads to icing. Change them every 1–3 months.
2. Clear the Area Around the Outdoor Unit
Keep at least two feet of space on all sides. Shovel snow, leaves, and other debris after every storm.
3. Inspect Coils and Fins
Clean the outdoor coil on a regular basis, using a soft brush or coil cleaner to assure good heat transfer.
4. Check the Drainage Path
Ensure water can drain away freely from the base of the unit to prevent refreezing.
5. Schedule Professional Maintenance
Have your HVAC technician service the system before winter. They’ll clean components, test sensors, check refrigerant, and verify defrost cycle timing.
6. Install a Cold-Climate Heat Pump (If Needed)
If you live in an area with cold winters, consider upgrading to a variable-speed or cold-weather-rated heat pump that can handle the low temperatures more effectively.
How Long Does a Heat Pump Take to Defrost?
A defrost cycle usually lasts anywhere from 5 to 15 minutes. During this time, you may notice:
• The fan outside stops spinning.
• Steam rising from the unit (that’s normal).
• Temporary lowering of the heating performance.
If your unit remains frozen beyond 30 minutes or doesn’t resume heating afterward, that means the defrost system needs servicing.
Frequently Asked Questions
1. Should I turn off my heat pump if it freezes up?
Yes. Immediately shut it off to prevent damage, and then follow the defrosting steps above. Operating it frozen can burn out the compressor.
2. How do I manually force the defrost cycle?
Some models provide the option for manual defrost through the control panel; however, if you’re not familiar with your system, it’s best to leave that up to a technician.
3. Can freezing damage the heat pump?
Yes. Continuous freezing and thawing can bend fins, crack coils, and shorten compressor life.
4. How often should my heat pump defrost in winter?
Typically every 30–90 minutes, depending on temperature and humidity. Frequent or constant defrost cycles indicate an issue with the control or sensor.
5. Does outdoor placing affect freezing?
Absolutely, heat pumps that are installed under roofs or near downspouts may collect excess water that freezes. Make sure to provide adequate drainage and shelter without blocking airflow.
Final Thoughts
If your heat pump has frozen during winter, take it for a warning, not some seasonal discomfort. The sooner you address it, the easier it will be-and cheaper, too.
First things first: clean the filter, clear any blockages from the unit surroundings, and ensure the fan turns without hindrance. If the problem persists with ice buildup, schedule professional HVAC service to inspect the defrost cycle, the refrigerant level, and sensors.
With regular care and a bit of attention, your heat pump will stay ice-free, efficient, and ready to keep you warm — no matter how cold it gets outside.
