Heat Pumps Defrost Cycle Demystified

One of the most frequently asked questions is the function of a Heat Pumps Defrost Cycle. It is useful to familiarise yourself with the reasons why this may occur, and when/if you should suspect a problem.

Defrost mode will automatically activate if ice has formed on the coil of your outdoor unit, due to the airs moisture freezing when temperatures drop to 0°C or below. Defrost mode works to regulate the airflow and restore full efficiency to the unit.

There are other factors that may induce Defrost Mode, including:

  • Outdoor temperature and humidity
  • Amount of heat the unit is trying to deliver
  • Condition of the heat pump

The length of cycle varies between 5 – 10 minutes, depending on the trigger. Regardless of time, be sure not to interrupt Defrost Mode, as restarting during or shortly after the cycle can cause damage to the unit and compromise its performance.

When Defrost Mode is initiated the indoor fan will slow, causing the pump to stop heating. The outdoor fan will also stop, but the compressor will continue to run. Defrost cycles should not occur more than every 30 – 40 minutes, and can only be completed when the unit has been running for at least 35 minutes.

If your heat pump is defrosting more regularly than it should, one of the following may apply:

  • The unit could be undersized for the space it needs to heat, however this should be initially checked by the installation company
  • A fault may have occurred
  • Maintenance is required – For example, cleaning the filter or making sure the heat exchanger is not blocked
  • You may be operating it incorrectly – Consult the instruction manual to make sure you’re following the appropriate steps

If you can’t fix the problem yourself, please don’t hesitate to call us on 0800 303 884

By maintaining your heat pump correctly, you can minimise the frequency of Defrost Mode occurring unnecessarily. Simple solutions such as, installing insulation under floors and in the walls and ceilings, or keeping doors and curtains closed, places less stress on your heating unit and prevents the rate of Defrost Mode in cold conditions.

Related Reads:
Cost of Running Heat Pumps

Beginners Guide to Heat Pumps

Choosing between HRV and a Heat Pump




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