A heat pump (HP) can sometimes become covered in frost, particularly during cold, wet periods. This phenomenon is normal up to a point, but when it becomes too frequent or persistent, it can interfere with the unit’s operation, and even lead to breakdowns. Here’s how to identify the causes and implement effective solutions.
Why does a heat pump frost?
Outdoor unit icing occurs when moisture in the ambient air condenses on the heat exchangers and then freezes, especially if the outdoor temperature is close to 0°C. This happens more often in heating mode, as the outdoor evaporator becomes colder than the ambient air. A little frost is therefore natural, but a well-tuned heat pump should defrost automatically.
Check that the defrost cycle is operating correctly
Most heat pumps are equipped with an automatic defrost cycle that temporarily reverses operation to warm up the outdoor unit. If this cycle is too short, too far apart or absent, frost will accumulate. In this case, have the unit checked:
- thermostat or temperature sensor
- the electronic board that controls the cycle
- correct operation of the reversing valve
This type of malfunction can usually be detected by annual maintenance.
Improving de-icing water drainage
When water from defrosting stagnates under the unit, it can refreeze and aggravate the problem. It is important to :
- provide a drainage slope under the unit
- install a drip tray with an antifreeze resistor
- check that drain openings are not blocked
Good evacuation limits the appearance of secondary frost under the machine.
Adapting the location of the outdoor unit
A poorly exposed or poorly ventilated installation is conducive to icing. To improve the situation :
- avoid overly shaded or north-facing areas
- clear obstacles around the unit to promote air circulation
raise the heat pump to protect it from ground humidity
In some cases, it may be necessary to relocate the unit.
Provide additional heating if necessary
At very low temperatures, the heat pump can reach its limits. If frost forms systematically in extreme cold, adding auxiliary heating can relieve the heat pump and limit defrosting phases. Some models already include an electric resistance for these situations.
Conclusion
A heat pump that frequently ices up is not inevitable. By ensuring proper maintenance, checking the defrost cycle, taking care of the installation and adapting the system to the rigors of the local climate, it is entirely possible to avoid frost-related malfunctions and guarantee optimal operation throughout the winter.
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