Key takeaways
- A small amount of frost on the outdoor unit during cold winter mornings is perfectly normal. Modern heat pumps automatically remove this frost using a defrost cycle.
- Heavy ice buildup, however, or ice forming on the indoor unit usually indicates that something isn't working as it should.
- When heating your home, the outdoor unit absorbs heat from cold outside air.
A small amount of frost on the outdoor unit during cold winter mornings is perfectly normal. Modern heat pumps automatically remove this frost using a defrost cycle.
Heavy ice buildup, however, or ice forming on the indoor unit usually indicates that something isn't working as it should.
Frost During Winter Is Normal
When heating your home, the outdoor unit absorbs heat from cold outside air.
Moisture in the air naturally freezes onto the outdoor coil. Every so often the unit temporarily switches into defrost mode to melt this frost before returning to normal heating.
This cycle is completely normal.
Ice That Doesn't Disappear
If thick ice remains on the outdoor unit for hours or continues to build, there may be an underlying fault.
Possible causes include:
- Low refrigerant.
- Faulty defrost controls.
- Sensor problems.
- Outdoor fan issues.
- Restricted airflow.
Ice on the Indoor Unit
Ice should never build up on the indoor coil.
This is often caused by:
- Dirty air filters.
- Blocked airflow.
- Refrigeration faults.
- Low refrigerant.
As the ice melts, water may begin leaking from the indoor unit.
Keep Airflow Clear
The outdoor unit needs unrestricted airflow.
Avoid stacking items against it or allowing leaves, vegetation or debris to block the coil.
Likewise, keep furniture and curtains clear of the indoor unit.
Annual Servicing Helps Prevent Problems
Routine servicing allows technicians to check refrigerant performance, clean coils, inspect sensors and confirm the defrost system is operating correctly.
Many freezing problems develop gradually and are easier to correct when found early.
When to Call Holmes Services
Arrange a service if:
- Ice remains on the outdoor unit after several hours.
- The indoor unit freezes.
- Heating performance has dropped.
- Water begins leaking indoors.
- The system displays an error code.
Frequently asked questions
Is frost on the outdoor unit normal?
Yes. Light frost during winter heating is expected and should disappear during defrost.
Should I chip the ice off?
No. Tools can easily damage the aluminium coil and refrigerant pipes.
Will cleaning the filters help?
Dirty filters can contribute to indoor icing, so regular cleaning is recommended.
Need practical advice for your system?
Holmes Services helps Auckland homeowners and businesses with heat pumps, ventilation, refrigeration and indoor comfort issues.