Air source heat pumps (ASHPs) have become a popular choice for heating homes in the UK. They’re energy-efficient, environmentally friendly, and work well in a variety of settings. But like any mechanical system, they’re not immune to the occasional issue. Whether you’re a homeowner or a property manager, understanding how to identify and resolve common problems can save you time, money, and unnecessary stress.
In this post, we’ll explore some of the most frequent problems people face with air source heat pumps and how to troubleshoot them effectively. The goal isn’t to turn you into an engineer but to give you enough know-how to recognise warning signs and take appropriate steps
whether that means fixing the issue yourself or knowing when to call in a professional.
1. Heat Pump Not Turning On
One of the first signs something might be wrong is when the unit doesn’t turn on at all. This can be frustrating, especially during colder months when you rely on it for warmth.
Things to check:
- Power supply: This may sound obvious, but start by checking the power. Make sure the heat pump is plugged in, and check the circuit breaker hasn’t tripped.
- Thermostat settings: If the thermostat isn’t set correctly, the unit might not turn on. Double-check the settings, and ensure it’s calling for heat.
- Timer or programming: Some systems have timers set for certain times of the day. Make sure it’s not programmed to be off during the time you’re trying to use it.
If all these are fine and the unit still won’t power on, there might be a more complex electrical issue, in which case it’s best to call a professional.
2. Poor Heating or No Heat at All
When the system runs, but the house doesn’t get warm, this typically indicates a performance-related issue. The cause could be mechanical, environmental, or maintenance-related.
Possible causes:
- Dirty filters or coils: A clogged filter or dusty coil can reduce the unit’s efficiency. Cleaning or replacing them can help restore performance.
- Incorrect settings: Check the mode on your system—it might be set to cooling or fan-only mode.
- Outdoor temperature: While air source heat pumps are effective in cold climates, their efficiency does decrease as the temperature drops. Some models struggle more than others in freezing conditions.
What to do:
Try cleaning the filters first—it’s a simple fix. If that doesn’t work, have a technician from ServiceMy run a full inspection, particularly if the issue keeps recurring.
3. Unit Frequently Turns On and Off (Short Cycling)
Short cycling happens when the system starts up, runs for a short time, and then shuts off repeatedly. It’s inefficient and can wear out components faster.
Why it happens:
- Oversized unit: If the system is too powerful for the space, it heats up quickly and shuts down before completing a proper cycle.
- Thermostat location: If the thermostat is too close to the unit or a heat source, it may misread the actual room temperature.
- Dirty filters or blocked airflow: Restricted airflow can also cause short cycling.
Suggested fix:
Try relocating the thermostat if it’s in an inconvenient location. Otherwise, get the unit serviced to check for issues with sizing or internal components.
4. Frozen Outdoor Unit
In winter, it’s common to see a layer of frost or ice on the outdoor unit. A small amount is normal, but if the whole unit is frozen solid, that’s a problem.
Potential causes:
- Faulty defrost cycle: Heat pumps have a defrost mode to melt accumulated ice. If that fails, ice can build up and block airflow.
- Poor drainage or airflow: Water that cannot drain properly will refreeze and exacerbate the problem.
What to do:
- Check that the unit is draining correctly and that nothing is blocking the airflow.
- Switch the system to defrost manually if your model allows.
- Don’t try to chip away the ice yourself—it’s easy to damage the fins. Instead, turn off the system and let it thaw naturally before restarting.
If this issue persists, the defrost sensor or control board may need to be replaced.
5. Unusual Noises
All heating systems produce some noise, but loud banging, rattling, or hissing can indicate potential trouble.
Different sounds and their meanings:
- Banging or clanking: This could be a loose fan blade or an issue with the compressor.
- Hissing: Often related to a refrigerant leak or high-pressure issue.
- Buzzing: This might point to an electrical fault or a failing motor.
Next steps:
Turn off the system and refrain from using it until the source of the noise is identified. If you suspect a refrigerant leak, don’t attempt to handle it yourself—it’s best left to a trained professional.
6. Rising Energy Bills
If your energy bill is climbing but your usage hasn’t changed, it could be due to a fault in the heat pump’s performance.
Likely causes:
- Dirty components: Reduced efficiency due to dirt and dust causes the unit to work harder.
- Refrigerant levels: Low refrigerant can reduce heating power and increase energy use.
- Old age: Systems that are over 10 years old naturally lose efficiency.
What you can do:
- Schedule a performance check.
- Keep up with regular filter changes.
- Track your energy use to spot patterns early.
7. Water Leaks
Although air source heat pumps don’t use water to heat, you might see puddles around the unit. This could be caused by condensation or drainage issues.
Check for:
- Clogged drain line: Blockages can cause water to back up and leak out.
- Improper installation: If the unit isn’t level, water might not drain properly.
Try clearing the drain pan and line. If water continues to appear, it may need inspection and reinstallation.
Routine Maintenance Tips
To prevent many of these problems from cropping up in the first place, regular maintenance goes a long way. Here’s what you can do:
- Clean or change filters every 1–3 months.
- Keep the outdoor unit clear of leaves, snow, or debris.
- Have the system inspected annually.
- Check insulation on refrigerant lines.
- Make sure fans and vents are unobstructed.
A yearly health check is especially important before the winter season kicks in. This helps spot minor problems before they become major ones.
When to Call a Professional
Some tasks are suitable for DIY checks, but others need proper expertise. You should consider calling a professional if:
- There’s a refrigerant leak.
- Electrical components are involved.
- The issue recurs even after basic troubleshooting.
- You’re unsure or uncomfortable doing it yourself.
Proper diagnosis and repair not only solve the problem faster but also keep the warranty valid and the system safe.
Final Thoughts
Air source heat pumps are a brilliant solution for sustainable home heating—but like all systems, they benefit from occasional attention. Many common issues can be resolved with straightforward troubleshooting, while others may require professional support.
Staying informed and proactive helps keep the system running smoothly and efficiently throughout the year. Whether you’re facing a noisy unit, low heat output, or just want to get ahead of potential faults, knowing what to look for is your best line of defence.
Regular maintenance, good habits, and timely checks can keep your system running at its best—and your home warm and comfortable when it matters most.
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