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Why get a heat pump?

  • Stop relying on gas
  • Slash your carbon footprint by up to 44%
  • Pair your heat pump with solar panels

7 Problems With Heat Pumps and How To Solve Them

Badly calibrated thermostats are a common source of heat pump problems

Refrigerant leaks can cause heat pumps to fail, or the outdoor unit to ice up

Obstructions on the outdoor unit can lead to an overworked heat pump

Given that heat pumps cost around £10,000, you’d rather they not break down. Unfortunately, heat pumps aren’t immune from problems. However, most issues are relatively easy to fix, and don't require the whole heat pump to be replaced.

We’ll go over each problem, its potential causes, and the solutions in this article, so you can feel confident about owning a heat pump.

Don’t have a heat pump, or want to replace yours? We can help. Simply fill in our short form, and we’ll pass your details onto our network of heat pump installers. They’ll reach out to you with their best prices.

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outdoor unit of a heat pump being worked on by a technician in red uniform

The 7 problems with heat pumps

We’ve rounded up seven common problems that occur with heat pumps, so you can know what to look out for. The most common problems are:

  1. The heat pump’s not heating or won’t turn on
  2. The heat pump is constantly running
  3. The heat pump isn’t going through its cycles correctly
  4. The heat pump’s outdoor unit is icing up
  5. The heat pump has an odd smell
  6. The heat pump is making strange noises
  7. The heat pump’s indoor units are leaking (air-to-air heat pumps)

We’ll go into more detail about each problem and how to solve it in the sections below.

1. The heat pump isn’t heating or won’t turn on

If a heat pump isn't heating your home, you’re likely to notice right away. This could mean one of several things is wrong, from the thermostat, the radiator valves (or air ducts if you have an air-to-air heat pump), the electrical supply, the refrigerant, or the outdoor unit.

Malfunctioning thermostat

If the heat pump isn’t heating, it could be because of a problem with the thermostat. The first thing to do is check that the thermostat is set to ‘heat’ and set at the correct temperature.

If it’s set at the correct temperature, but there’s still no heat, it could be that the thermostat is out of battery (if it’s battery operated), or that you have a tripped circuit. In both cases, either replace the batteries or check your circuit breaker.

If that still hasn’t solved the issue, it’s possible the thermostat isn’t calibrated correctly, in which case you should contact a professional to get it fixed.

Closed radiator valves or blocked air filters

If you have an air or ground source heat pump, there could be an issue with your radiators. Make sure that the control valves (which are usually on one side of the radiator) are open.

If you have an air-to-air heat pump, check the air filters in your ducts. Dirty air filters could be blocking hot air from entering the home. If they seem dirty, try cleaning them with water, or get them replaced.

Loss of electrical supply to the heat pump

If your heat pump isn’t heating, it could be because it’s lost its electricity supply.

First, check that the switch for both your indoor and outdoor unit is set to ‘on’. If both units are set to ‘on’, next, check your circuit breaker for a tripped circuit.

If you’ve checked the switches and the circuit breaker, and neither are at fault, there could be a more complicated issue with the electricity supply. This is when it’s time to call a technician.

Low or leaking refrigerant

Refrigerant is crucial for the heat pump to transfer the heat it gathers from outside into your home.

So if your heat pump isn’t heating, it could be because the refrigerant levels are low. This could be because of a leak, or another issue. Either way, it’s best to call a technician to fix any potential leaks and replace the refrigerant.

The outdoor unit is blocked

If you have an air source heat pump or air-to-air heat pump and something is blocking the outdoor unit from pulling heat from the outside air, it might not be able to heat your home effectively.

Check your outdoor unit for buildups of debris, such as leaves, snow, or ice, and clear them away. Also make sure no large piece of garden equipment has been placed against your outdoor unit.

If that doesn’t solve the issue, it’s time to call a technician.

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2. The heat pump is constantly running

Heat pumps aren’t typically meant to be constantly running in order to maintain a set temperature. One of many things could be causing this, such as incorrect thermostat settings, a heat pump that's the wrong size, leaking refrigerant, or temperature extremes.

The thermostat is set at too high a temperature

If the heat pump is working non-stop, it might be because you’ve set your thermostat at too high a temperature, and the heat pump is struggling to keep up. Ideally, in the winter the thermostat should be set between 18ºC and 22ºC.

If your home doesn’t feel warm enough at this setting, it might be time to look into getting better insulation, since a constantly running heat pump will drive up your electricity bills.

The heat pump is the wrong size for your property

Another reason the heat pump might be running constantly is because it’s not the right size for your home. Heat pumps with too small a capacity will have to work overtime to heat a large home. If that’s the case, you’ll need to switch your heat pump out for a large model.

The refrigerant is leaking

Refrigerant plays a vital role in transferring heat from the outside air or ground to inside your home. A leak will reduce the level of refrigerant in your heat pump, and cause it to work harder to meet the thermostat’s heat setting.

If this is the issue, you’ll need to call a technician to fix the leak and replace the refrigerant.

It’s very cold (or hot) outside

Another reason why your heat pump might be running all the time is simply that it’s a particularly cold day out, and the heat pump has to work overtime to draw heat from the air or ground.

This is more likely to happen with air source heat pumps or air-to-air heat pumps, since ground source heat pumps fare better in very cold weather conditions – when the outside air is at 0ºC, the ground is usually at 10ºC.

Air-to-air heat pumps double up as air conditioning units in the summer, and so they might also run constantly during a heatwave as they struggle to cool the home.

Unfortunately there’s not much you can do if temperature extremes are causing your heat pump to work constantly. You can, however, reduce the risks of this happening by getting the right size heat pump for your home, and properly insulating your property.

Find out more about how heat pumps work in cold weather.

outdoor unit of heat pump against stone wall in snowy garden

3. The heat pump isn’t going through its cycles correctly

If you’ve set your heat pump to heat your home at specific times, and it's not following this preset cycle, this could mean it’s overheating, or that there’s a fault with the thermostat.

The heat pump is overheating 

If the heat pump overheats, it could stop working and not finish a heating cycle, or not turn on for the next cycle. Heat pumps can overheat if their airflow is blocked by a dirty filter.

To solve this problem, open the unit and check to see if the filter needs cleaning or replacing.

There’s a fault with the thermostat

As with many other heat pump problems, a faulty thermostat might be the main cause. If the thermostat hasn’t been calibrated correctly, it could cause the cycle to end before the desired temperature has been reached.

If that’s the case, you’ll need to get a technician in to recalibrate the thermostat or replace it.

4. The heat pump’s outdoor unit is icing up

Heat pumps are designed to work in cold temperatures, and it’s normal for them to get covered by ice or snow in the winter.

However, if you notice that ice keeps building up on and inside your heat pump’s outdoor unit, it could indicate a problem with the defrost function or the outdoor fan, low refrigerant levels, or lack of airflow.

A broken defrost function

Most heat pumps have a defrost function to prevent their inside freezing up in the winter. This function is usually automatic, so if the heat pump is freezing it could indicate a fault with the function.

To get this fixed, you’ll need to contact a technician.

A problem with the fan in the outdoor unit

The outdoor unit of an air-to-air or air source heat pump typically has a fan that helps draw air from outside to be converted into heat for your home.

If this is broken or moving too slowly, the refrigerant will absorb less heat, which means the inside of the unit is more likely to freeze.

Malfunctioning fans need to be fixed by a professional.

The refrigerant is low

Low refrigerant can be the source of many heat pump problems, including why the outdoor unit is icing up.

Low refrigerant, just like a faulty fan, can prevent the heat pump from generating enough heat to prevent ice from building up inside of it at below 0 ºC temperatures.

If that’s the case, you should have the refrigerant replaced by a technician.

Something’s blocking the airflow to the unit

If leaves or other debris build up on the heat pump’s outdoor unit, this can block its airflow, and cause it to slow down.

This increases the chance of ice buildup. Placing objects too close to the front of the heat pump can also lead to lack of airflow, such as parking a car right in front of the unit.

Here the solution is simple, clear the debris or move the object that’s in front of the unit.

5. The heat pump has an odd smell

If you notice an odd smell coming from either the inside or outside unit of your heat pump (or from your air ducts if you have an air-to-air heat pump) it could signal the presence of mould, a pest invasion, or faulty electrical wiring.

Mould growing inside the unit

A musty or earthy smell coming from the heat pump’s outdoor unit (or the air ducts if you have an air-to-air heat pump) could indicate mould growth.

A little bit of mould on the outdoor unit is normal, and is something you can clean away yourself with a damp cloth. However, if it becomes extensive, the unit might require professional cleaning, or need to be replaced entirely.

Mould in the air ducts of homes with air-to-air heat pumps requires professional attention, as removing it is difficult, and it can lead to health problems.

Dead animals inside the outdoor unit

Nature happens, and a rotting smell coming from the outdoor unit could mean that a small animal has crawled inside and died.

If you think this is the case, you can open up the unit and remove the carcass yourself. If you’re too squeamish to do this, you can always hire a professional.

Severe electrical issues

If you notice a smoky or fishy smell coming from any part of your heat pump system, it could mean the motor is overeating, or there’s a problem with the wires.

Either way, the best thing to do is to turn off the heat pump via its switch on the circuit breaker, and call a technician to take a look inside the heat pump.

6. The heat pump is making strange noises

If the heat pump is making strange noises, or much more noise than usual, it could mean there’s a loose piece of hardware, the motor has an issue, or the heat pump is working too hard.

The heat pump is making a rattling noise

If the outdoor heat pump unit is making a rattling noise, this could mean a small piece of hardware is loose inside the unit, or that the unit is not properly screwed shut.

Firstly, make sure the heat pump unit is screwed tightly shut. If the rattling continues, that means something is loose inside, and a technician needs to come and fix it.

The heat pump is making a grinding sound

If the heat pump is making a grinding or squeaking sound, this could mean the motor or coils inside the unit are wearing out.

If this is the case, turn off the heat pump via the circuit breaker straight away, and call a technician. Motor problems can be dangerous, so it’s best not to take any risks.

The heat pump is being louder than usual

If the heat pump isn’t making odd noises, but is being louder than it usually is, this means it's working harder than usual.

This could be due to the weather – it’s a very cold day, for example – but it could also mean you have the wrong size heat pump for your home.

If you think that’s the case, call a professional to have the heat pump and your home assessed.

7. The heat pump’s indoor units are leaking (air-to-air heat pumps)

It’s normal for the outdoor unit of a heat pump to leak slightly, since condensation can build up inside the unit.

However, if you have an air-to-air heat pump, and you notice an indoor unit or pipe leaking, this could indicate a problem with the refrigerant, or a clogged drain line.

Low or leaking refrigerant

Low or leaking refrigerant can cause ice to build up deep inside the air-to-air heat pump’s system. When the ice melts, it will cause a leak.

If you notice this happening, get the heat pumped checked by a professional.

A clogged drain line

Air-to-air heat pumps have drain lines specifically designed to evacuate water caused by condensation. If the drain gets clogged by debris, it can cause water to build up and start leaking into other parts of the system.

You can try to unclog the drain yourself, but it’s safer to get a technician to take a look at the unit.


Heat pumps are wonderful pieces of equipment, and using one to heat your home instead of a gas boiler will lower your carbon footprint.

However, we'd be lying if we said they didn’t have any faults; problems can occur with any piece of machinery, including heat pumps.

Luckily, you’ve read this article, so you know what to do if you have a heat pump problem.

If you don’t yet have a heat pump, and would like to get one, we can help. Just fill in our short form with a few details, and we’ll pass them onto professional heat pump installers. They’ll be in touch with quotes.

Heat pump problems: FAQs

Heat pumps last 20-25 years on average. That’s around a decade more than gas boilers, which typically last 10-15 years.

And that’s not all. The underground components on a ground source heat pump can actually last up to 70 years, while the above ground units need to be changed sooner.

Find out how heat pumps stack up against gas boilers by going to our page, Heat Pumps vs Gas Boilers.

Yes, a heat pump can heat a whole house. Heat pumps are designed to be integrated into your existing heating system of radiators, underfloor heating, or air ducts (if you get an air-to-air heat pump).

This means that they'll provide heat to every room in the house that has a heat dispenser, such as a radiator, installed.

Air source heat pumps use electricity to convert heat from the air into heat for your home, so it’s normal to see an increase in your electricity bills when you switch from gas heating to electric heating.

However, if you notice an unusual spike in your electricity usage, it could indicate that there’s a problem with your heat pump. In this situation, it’s a good idea to get it serviced by a professional so they can tell you what’s wrong and fix it.

Written by:
Tatiana has written about multiple environmental topics, including heat pumps, energy-efficient household products, and solar panels. She is dedicated to demystifying green tech to make eco-friendly living more accessible.
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