Top 5 common issues with Air Source Heat Pumps

Air Source Heat Pumps are an increasingly popular, sustainable and economical way of heating homes in the UK – but as with any system, they experience the occasional blip, especially if the unit isn’t set up or serviced properly. 

When heat pumps go wrong, it’s usually because of a few common reasons. Troubleshooting these problems will help you keep bills down and get the heat pump up and running quickly.

The most common issues with Air Source Heat Pumps

This is one of the most common complaints, where your system is running but takes an age to reach the desired temperature.

The most common issues with Air Source Heat Pumps

Lack of heat or low performance

This is one of the most common complaints, where your system is running but takes an age to reach the desired temperature.

Common causes include:

• Dirty or blocked air filters
• Low refrigerant levels
• Thermostat or control issues
• Poor airflow due to blocked vents or ducting
• An undersized system or poor insulation

What to look out for:

• Rooms that feel cooler than usual
• Your system is running constantly or switching off too quickly (short cycling)
• Energy bills are creeping up for no reason

What to do:

• Check and clean the air filters
• Make sure your thermostat is set correctly and hasn’t lost connection
• Clear any obstructions from the vents or the outdoor unit
• If problems persist, call a qualified technician – low refrigerant or flow rate issues need urgent professional attention

Icing on the outdoor unit

Frost on your outdoor unit during winter is quite normal and can be handled by the heat pump, but if the unit has a heavy ice build-up or is frozen over, something’s not working properly.

What causes excess icing?

• Poor airflow around the unit
• Blocked or dirty coils
• Low refrigerant levels
• A malfunctioning defrost cycle
• Obstructed or snow-covered vents

Why it matters:

• Ice build-up restricts airflow, reducing its efficiency
• Your system may stop heating altogether
• Long-term strain can damage components

What to look out for:

• Keep the area around the outdoor unit clear of obstructions
• Don’t try to chip off the ice – this could cause more damage
• Gently clear loose snow or frost with warm water or airflow
• If the problem persists, get the system checked by a professional, especially the defrost cycle and refrigerant charge

Strange or excessive noise

If your air source heat pump starts making odd or excessive noises, get it investigated. Buzzing, rattling, hissing, or grinding sounds usually mean something’s loose, worn out, or not running as it should.

Common causes include:

• Loose panels or components
• Debris in the fan or outdoor unit
• Worn bearings or motor issues
• Fan imbalance or misalignment
• Refrigerant leaks (often signalled by a hissing noise). If this is the case, call a professional immediately

What to do:

• Switch the unit off and check for debris or loose covers
• Tighten any visible panels or screws (if safe to do so)
• Keep the area around the outdoor unit clear
• If noise persists or worsens, contact a qualified engineer, especially for refrigerant or electrical components

Catching the cause early will help prevent further damage and expensive repairs.

Thermostat or control issues

Sometimes the issue may lie with the thermostat or control system. If your heating feels inconsistent, won’t respond to adjustments, or cycles on and off at odd times, it could be a control problem.

Common causes include:

• Incorrect thermostat settings
• Dead batteries or lost connection (for wireless models)
• Compatibility issues between smart thermostats and the heat pump
• Sensor errors or calibration faults

Signs to look out for:

• Your system is not responding to changes in temperature settings
• Heating feels erratic or doesn’t match the setpoint
• Your system turns on and off too frequently

Solution:

• Check the thermostat settings and reset if needed
• Replace batteries in wireless models
• If you’ve recently installed a smart control system, check compatibility
• If controls continue to behave oddly, consider an upgrade or arrange a visit from a technician

Modern heat pumps work best with smart, responsive control systems. Regular checks and occasional upgrades will keep everything running smoothly and efficiently.

Installation and sizing errors

Some of the most persistent heat pump problems are inherited from the start. If your system was poorly installed or incorrectly sized, you might experience ongoing issues.

Common installation and sizing problems include:

• The unit is too small (or too large) for your property
• Pipework or ducting is poorly laid out or undersized
• The outdoor unit is installed in a location that’s too sheltered or blocked
• The refrigerant charge is incorrect from the outset
• Poor integration with radiators, the hot water system, or controls

Signs of underlying design faults:

• The system struggles to function
• Frequent short cycling
• High energy use despite good insulation
• Uneven heating across rooms

What to do:

• If your system has had ongoing issues since installation, consider a full performance assessment
• Contact a trusted provider to check the system’s sizing, placement, and performance
• Prevent future issues through booking certified engineers for upgrades or replacements

Expert installation and regular servicing are key to long-term efficiency and reliability, with fewer costly surprises down the line.

Unusual smells coming from your heat pump

If you notice musty, burning, or chemical smells from your heat pump, it’s a sign that something’s not right.

Possible causes include:

• Mould or mildew build-up in ducts or filters
• Electrical issues or overheating components
• Refrigerant leaks (which emit a sharp, sweet, or chemical odour)

Solution:

• Turn your system off if the smell is strong or unusual
• Clean or replace the filters if you suspect mould
• Contact a professional for persistent burning or chemical smells

Unusual smells aren’t always serious but shouldn’t be ignored.

How to prevent the most common heat pump problems

Most issues can be avoided with simple, regular maintenance and care. Here’s how to keep your system in great shape:

• Clean or replace filters regularly

Dirty filters restrict airflow, reduce efficiency, and strain the system. Check them regularly, especially during heavy use.

• Keep the outdoor unit clear

Clear away all obstructions from the external unit to maintain proper airflow and prevent ice buildups.

• Book annual servicing

A yearly service by a qualified engineer will keep refrigerant levels correct, components clean, and address potential faults.

• Use the right controls

Set your thermostat to steady, consistent temperatures. Avoid making constant manual adjustments and use smart controls if possible.

• Act quickly on unusual signs

If your system gets noisy, underperforms, or seems to be using more energy, don’t ignore it. Catching issues early will prevent major repairs later.

With routine maintenance and timely professional support, your heat pump will run efficiently, comfortably, and reliably all year round.

Want peace of mind that your system’s in good hands?

Whether you’re dealing with one of the common issues we’ve covered, or simply want to stay ahead of potential problems, ServiceMy offers professional repairs, responsive emergency call-outs, and tailored service plans to keep your system running smoothly all year round.
Get in touch today to protect your heating, avoid unnecessary costs, and enjoy reliable home comfort, whatever the season