How to Defrost a Heat Pump

How to Defrost a Heat Pump

In plain terms, a heat pump transfers heat from one point to another. In this guide, we will briefly look at how a heat pump works and how frost can affect its efficiency. We will also consider three practical ways of defrosting your heat pump, especially if your heat pump is freezing up in the winter.  

We will use the air source heat pump for our illustration. 

An air-source heat pump harvests heat from the air outside your house and channels it into your room via dedicated coils and ducts. It’s able to absorb heat even from extremely cold air; thus, it is considered one of the most energy-efficient heat pumps. 

How a Heat Pump Works

In order to acknowledge the need to clear frost from your heat pump, it is important to understand how it works. You also need to recognize the effects of frost on your heat pump.

Air source heat pumps operate more like air conditioners, except that the air and refrigerant in a heat pump flow in the opposite direction, thanks to the use of reversing valves. Think of a refrigerator’s cooling system turned inside out. 

An air conditioner absorbs heat from the air inside your house and blows it outside. But the heat pump picks heat from the air outside and channels it into your house. 

A heat pump has two major parts: outdoor and indoor units. The outdoor unit consists of a coil and a fan. Usually, the fan blows air over the coil, while the coil, in turn, absorbs heat from the air. 

The absorbed heat is carried in a refrigerant through a loop of coils into the compressor. Here, the compressor amplifies the heat by pressing it. Subsequently, the temperature gets hot enough to vaporize the refrigerant. 

The hot gaseous refrigerant is channeled through another loop of coils into the indoor unit. From here, a fan blows air over the hot coils, funneling it into ducts that eventually vent hot air into your room. 

How Cold Weather Causes Heat Pump Frost

When the external air is moderately cool and your heat pump is on heating mode, the outdoor coil evaporates moisture easily. But when the air gets colder and moist, the outdoor coil may gather frost. This layer of frost alters the pump’s optimal working conditions, hence negatively affecting its efficiency. 

How to Prevent Heat Pump Frost

During winter weather, frost is inevitable. But maintaining the following conditions can significantly reduce the chances of your pump getting frozen.  

  • Install a heat pump with capacity corresponding to the heat demand of your home. 
  • Check and clean the filters regularly — if they are too clogged, replace them.
  • Keep the pump housing and the surrounding area clean, free from dust and debris.
  • Maintain efficient drainage around the heat pump.

Despite your best practices, it is still possible for you to have a frozen heat pump during extreme weather. Below are tips on how you can get it working efficiently again.

What to Do if Heat Pump is Frozen

Here’s how to defrost a heat pump. 

1. Run the Fan 

Run the fan for about an hour. Air, however cold, moving fast over frost can cause enough friction to induce thawing. 

If the air itself is too cold to liquefy the frost, set the fan to exhaust mode. In this state, the pump avails warm air from the coils to the fan. The fast-moving warm air running over the frost should thaw it away. 

Remember to turn the fan back to automatic mode immediately when the frost falls off. This method, however, should never replace the normal operation of your heat pump. It’s a stop-gap measure. 

It’s important to note that not all heat pump models have fans, which can be operated manually.

Therefore, you may have to consider the most applicable of the suggestions offered here. 

2. Engage Manual Defrost Cycle 

Modern heat pumps have an automatic defrosting system. But if your pump has a manual defrost switch, turn it on every time frost becomes a problem. 

If your pump is set to power-saving mode, it automatically shortens the defrost cycle in order to consume less electricity. This way, the pump terminates the defrosting process before the coils are free from frost. 

Disengaging the power-saving option will let the pump use its full capacity to get rid of all frost. You may save some money by running your heat pump on power-saving mode but, by doing so, you compromise its efficiency and durability. 

3. Move the Sensor Manually

If the heat pump’s automatics fail to self-activate, you may have to push the buttons yourself. For you to execute this task, you must be familiar with the thermostat or sensor.  

If you resort to this choice, follow this simple procedure:

  1. Locate the thermostat 
  2. Mark the manufacturer or original sensor position before you move it. This is important in case you need to restore it later. 
  3. Move the sensor close to the intake region. This is the point around which the automatic function sets the pump in order to switch it to the defrost cycle.

Common Mechanical Faults That May Cause Heat Pump Frosting

As the snow builds up during winter, it’s normal for your heat pump to get frozen up. Nevertheless, the pump is equally expected to engage self-thawing as part of its routine operation. If it isn’t defrosting even after trying the above steps, then it could have one or a combination of the following faults:

  • A faulty reverse valve
  • An opposite-running motor 
  • Exterior coil stuffed with dirt and other particles
  • A fan not revolving
  • A thermostat malfunction
  • Faulty wiring
  • Opposite fan installation with blades blowing air the other way 
  • A loose or slipping fan belt making a fan run slowly 
  • Insufficient refrigeration gas in the cylinder
  • A leaking coil or cylinder

Most of the faults mentioned here above are beyond the scope of a regular home-owner to fix. Therefore it is necessary to get an HVAC technician to carry out an accurate diagnosis and bring a sure resolution. 


Always operate your heat pump on the manufacturer’s settings. Keep the casing and surrounding surfaces clean. And to avoid electric shock, never thaw frost with hose water. Make it a habit of getting a qualified technician to regularly inspect your heat pump. 

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