Heat Pump Defrost Cycle
Is Your Heat Pump Making Strange Sounds? Here's What You Need To Know About Defrost Cycles
Have you noticed your heat pump making unusual noises during the cold weather? If you’re hearing gushing, low humming, or whooshing sounds, don’t worry—this is often a normal part of how your heat pump keeps running efficiently. One common cause is the defrost cycle, a crucial process that protects your system in winter. While these sounds can be a little concerning if you’re not familiar with them, they’re usually just a sign that your heat pump is doing its job.
What Is The Defrost Cycle?
When temperatures drop, moisture in the air can freeze on your heat pump’s outdoor coil. This frost can block airflow and reduce efficiency or damage. To fix this, your heat pump occasionally switches into defrost mode—a self-cleaning process that melts away ice and keeps your system running smoothly.
What exactly happens?
In heating mode, a heat pump extracts heat from the outside air and transfers it inside to warm your home or commercial space. When the ambient temperature outside gets very cold, the moisture in the air freezes on the outdoor unit's heat exchanger as the fan blows the air across it.
When the heat pump goes into defrost mode, it momentarily reverses operation and goes through the “cooling cycle.” This forces warm air through the outdoor coil, warming it temporarily to remove the frost.
What Happens To The Heat Pump During The Defrost Cycle?
In defrost mode you may notice the indoor unit temporarily stop heating, the indoor fan will stop or slow down depending on the model, you may feel some cold air and there maybe be some visual indication such as blinking lights on the indoor unit. The outdoor unit's fan will stop however the compressor will be running.
The sound your heat pump will make in defrost mode will differ depending on the make and model as well as the pipe length.
A normal cycle may take 10 - 15 minutes.
What Noises Are Normal During The Defrost Cycle?
During defrost mode, you might hear:
- Whooshing or gushing sounds: Caused by the system reversing operation.
- Low humming: The compressor is still running.
- Clicking or hissing: As valves switch and refrigerant flows change.
These sounds are usually nothing to worry about and are a sign that your heat pump is doing its job!
What Should You Expect?
- The indoor unit may stop heating briefly, and you might feel cooler air
- The indoor fan may slow down or stop
- You might see blinking lights on the indoor unit (a normal indicator)
- The outdoor fan will stop, but you’ll still hear the compressor running
- The entire defrost cycle usually lasts 10–15 minutes
When Should You Be Concerned?
If you notice:
- Loud banging, grinding, or unusual noises
- The defrost cycle lasting much longer than 15 minutes
- Persistent ice buildup after the cycle finishes
…it might be time to call a professional for a check-up.
Need Help? We're Here For You!
If your heat pump is frequently going into defrost mode, is defrosting for a prolonged period of time, or has a lack of heat, there may be an issue that requires diagnosis.
Call
03 366 1823 to book a diagnosis or maintenance appointment,
we're always happy to help keep your home warm and comfortable!
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