We know how stressful it is when your heat pump isn’t working, especially when you’re not sure where to start.
The good news is that most heat pump problems have a simple cause. This guide covers the faults we come across most often, what’s behind them, and the steps you can take before picking up the phone.
1. Your heat pump isn’t heating, or won’t turn on
If your heat pump has stopped heating your home, there are a few things worth checking before calling a technician.
Check your power supply first
Confirm that the switches on both your indoor and outdoor units are switched on. Then check your circuit breaker for any tripped switches.
If everything appears fine and there’s still no heat, there may be a more complex electrical fault. A technician will be able to diagnose it.
Check your thermostat
Make sure it’s set to ‘heat’ and the temperature is turned up. If it’s battery-operated, try replacing the batteries. A tripped circuit breaker can also cut power to the thermostat, so it’s worth checking that too.
If everything looks right but it’s still not working, your thermostat may need recalibrating. That’s a job for a professional.
Check your radiator valves or air filters
If you have a standard air source heat pump, check that your radiator control valves are open. They’re usually on one side of the radiator.
For air-to-air heat pumps, take a look at the air filters in your ducts. A build-up of dust and debris can block warm air from getting through. Clean them with water, or replace them if they’re beyond saving.
Low or leaking refrigerant
Your heat pump needs refrigerant to move heat from outside into your home. If levels are low, possibly due to a leak, it can’t do its job. A technician can check for leaks and top up the refrigerant.
Clear the outdoor unit
Take a look outside. Leaves, snow, or ice building up around the outdoor unit can stop it from drawing in heat effectively. Clear any debris and make sure nothing is blocking it.
If you’ve been through everything above and nothing has changed, it’s likely something that needs a professional eye. Call us on 01603 406 052 and we’ll help you work out what’s going on.
If your heat pump is more than a year old and hasn’t been serviced recently, that could be a factor. Our annual servicing visits cover electrical testing, function checks, fluid top-ups, and a full inspection.
It’s one of the easiest ways to catch small faults before they become bigger ones.
2. Your heat pump is constantly running
Heat pumps are designed to run for long periods, but not continuously. If yours won’t switch off, a few things could be behind it.
Your thermostat is set too high
If the target temperature is too ambitious, your heat pump will keep running trying to reach it. During winter, aim for somewhere between 18°C and 22°C.
If your home still feels cold in that setting, it may be worth looking at your insulation. A heat pump working harder than it needs to will push your electricity bills up.
Your heat pump may be too small for your home
A heat pump that isn’t sized correctly for your property will struggle to keep up, running constantly without ever quite getting there. If that’s the case, a replacement with a more suitable capacity may be the answer.
There could be a refrigerant leak
Refrigerant is what carries heat from outside into your home. If there’s a leak, levels drop and your heat pump has to work harder to compensate. A technician can find the leak, fix it, and top up the refrigerant.
The weather outside may be the cause
In very cold conditions, heat pumps naturally have to work harder to extract heat from the air or ground. There’s not much you can do about the weather, but having the right sized heat pump and good insulation will reduce how often this becomes a problem.
If you’ve checked the thermostat and nothing outside explains it, it’s worth getting a technician to take a look. A refrigerant leak or a sizing issue aren’t things you can diagnose yourself, and leaving either unaddressed will cost more in the long run.
3. Your heat pump is making strange noises
Most heat pumps hum quietly in the background. If yours has started making noises it didn’t before, something is usually worth investigating.
A rattling noise
Rattling from the outdoor unit usually means something has come loose. This could be the panel casing, mounting bolts, or a component inside the unit vibrating against the casing.
Start by checking that the unit is sitting level and securely fastened to its base. If the rattling continues, the source is likely internal and a technician will need to open the unit and track it down.
A grinding or squeaking sound
This points to friction somewhere it shouldn’t be. The most common causes are worn fan bearings or deterioration on the motor itself.
Both affect how the unit moves refrigerant around, which means the problem will get worse the longer it runs.
Switch the heat pump off at the circuit breaker and call a technician. Don’t leave it running.
In our experience, grinding and squeaking are the noises that most often lead to a repair if left too long. Rattling is usually more straightforward to fix, but it’s still worth catching early before it puts strain on other components.
It’s louder than usual, but no strange sounds
A general increase in noise without any specific sound usually means the compressor or fan is working harder than normal.
In cold weather this is expected, as the unit has to work harder to extract heat from the air.
But if the noise has gradually increased over time, it can indicate a drop in refrigerant pressure, a partially blocked coil, or a heat pump that isn’t matched well enough to the size of your home. A technician can check pressures, inspect the coil, and assess whether the system is sized correctly.
4. Your heat pump isn’t completing its heating cycles
If your heat pump is cutting out before your home reaches the right temperature, or skipping scheduled heating cycles entirely, there are two likely causes.
The unit is overheating
When a heat pump overheats, it will often shut itself down as a safety measure. This can interrupt a cycle mid-way, or prevent the next one from starting at all. The most common reason is restricted airflow, usually caused by a dirty or blocked filter.
Check the filter first. If it’s clogged with dust and debris, clean or replace it and see if the cycling returns to normal.
The thermostat isn’t reading correctly
If the filter is fine, the thermostat may be the issue. A thermostat that’s lost its calibration can tell the system the target temperature has been reached before it actually has, cutting the cycle short. This is less obvious to spot because the heat pump appears to be working, it’s just stopping too early.
A technician can test whether the thermostat is reading accurately and recalibrate or replace it if needed.
Worth knowing
Short cycling puts additional wear on the compressor over time. If you’ve noticed it happening regularly, it’s worth getting it looked at before it leads to a bigger repair.
5. Your heat pump’s outdoor unit is icing up
Some ice on the outdoor unit during winter is normal. Heat pumps are designed to handle cold temperatures, and a light frost on the casing is nothing to worry about. What you’re looking for is persistent ice building up on or inside the unit, which points to something that needs attention.
The defrost function isn’t working
Most heat pumps have an automatic defrost cycle that runs periodically to prevent ice building up inside the unit. If that function has developed a fault, ice will accumulate unchecked. This one needs a technician to diagnose and fix.
The outdoor fan isn’t running properly
The outdoor unit uses a fan to draw air across the refrigerant coil. If that fan is slow or not working, less heat gets absorbed from the outside air and the coil temperature drops, making ice formation much more likely. A professional will need to assess the fan and identify whether it needs repair or replacement.
Refrigerant levels are low
Low refrigerant reduces the amount of heat the system can absorb, which can cause the coil to drop below freezing and ice over. This often points to a leak elsewhere in the system. A technician can trace the source, carry out the repair, and recharge the refrigerant.
Something is blocking airflow to the unit
Leaves, debris, or objects positioned too close to the unit can restrict the airflow it needs to operate efficiently. This makes icing more likely, particularly in cold weather. Check the area around the unit and clear anything that’s built up or blocking the front. The recommended clearance is usually at least one metre on all sides.
Still having problems with your heat pump?
Most heat pump faults have a straightforward cause, and many can be resolved with a basic check before a technician needs to get involved. But some issues, refrigerant leaks, electrical faults, defrost failures, do need a professional eye.
If you’ve worked through this guide and something still isn’t right, we’re here to help. Our engineers are based in Norfolk and Suffolk and carry out diagnostic visits, repairs, and annual servicing across the region.
Many of the faults covered in this article – blocked filters, low refrigerant, fan wear, are things a routine service will pick up before they become a problem. Most manufacturers also require evidence of regular servicing to keep warranties valid, and it’s a condition of most heat pump grant schemes too.
We offer fixed price annual servicing with a site visit from one of our engineers, covering electrical testing, function checks, fluid top-ups, and a full visual inspection. We’ll also send you a reminder when your next service is due.
Call us on 01603 406052 or visit our Servicing and Support page to find out more.