Modern heat pumps constantly monitor their own operation and display error codes whenever they detect something that needs attention. And there’s no question that spotting one can be pretty worrying, especially if you think that your hot water or heating might be affected. But don’t let it cause you too much stress – an error code isn’t necessarily telling you that there’s a catastrophic problem. They’re not designed to panic you, but just to give you a heads-up that allows you to deal with a fault before it has a greater impact on your home’s comfort or your system’s performance.
Of course, this is why it’s so helpful to have advance warning of what these messages mean – it helps you understand what your heat pump is trying to tell you and the difference between an urgent problem and a minor one, especially if it’s not been serviced in a while. Here, we’ll detail ten of the most common heat pump error codes, what they usually mean, and the practical steps that you can take next.
Why heat pumps show error codes
As we’ve touched on above, when it comes to its own maintenance, your heat pump arguably does most of the hard work for you. Every day, it monitors temperatures, pressures, water flow, electrical components and communication between different parts of the system to make sure that everything is operating within its expected range. If one of those readings falls outside the limits that the manufacturer has programmed into the unit, the heat pump displays an error code.
All that means by the time an error code appears, your heat pump will have already carried out a series of automatic checks behind the scenes. Even in the most serious cases, there are still measures in place for your peace of mind – your heat pump may well temporarily limit its operation or pause completely because its built-in safety features have detected a condition that needs attention. That gives you more breathing room to look after your system while giving you a clear indication that something requires investigation.
How to read your heat pump error code
The first step is obviously to find the error code itself. Depending on your heat pump, it may appear on the main display panel, an indoor controller, or a companion app if your system includes smart controls. Most manufacturers make the code easy to find because it provides the quickest way to identify what your heat pump is trying to communicate.
Now, one important thing to bear in mind is that there isn’t a universal coding system. Every manufacturer uses its own coding system, so the same combination of letters and numbers can mean completely different things on different models. That’s why it’s always worth referring to your owner’s manual or the manufacturer’s guidance before taking any action.
Many heat pumps also use colour-coded alerts alongside their error codes. A yellow or amber warning usually indicates that the system has detected an issue that needs attention while allowing normal operation to continue. A red warning often signals a more serious fault or a condition that has triggered the heat pump’s built-in protective measures. Paying attention to both the code and the colour of the alert can give you a much clearer picture of what’s happening before you decide on your next step.
The 10 most common heat error pump codes, explained
Before we go into detail on the individual codes, it’s worth highlighting that not every heat pump error code needs an immediate response. Some are warning messages that allow your system to continue operating, while others indicate a more serious fault that may impact its performance or stop your heat pump altogether. Don’t forget to check your owner’s manual and the manufacturer’s guidance alongside this guide.
E1/F1 – Low Refrigerant
Low refrigerant is one of the most common heat pump faults, and usually means that the system doesn’t have enough refrigerant to transfer heat efficiently. Unlike fuel, refrigerant isn’t something that gets used up during normal operation, so this code often indicates a leak or a problem that needs professional attention.
There are a couple of different signs of low refrigerant – you may notice that your home takes much longer to reach the temperature you’ve set, or your hot water isn’t as consistent as usual, or your heat pump seems to run for longer periods without delivering the same level of comfort. Some homeowners might also notice a gradual increase in their energy bills as the system works harder to compensate.
Your heat pump may continue operating, but if the issue is left unresolved, that can place additional strain on the system.
E2 – High Pressure
A high pressure code means that the refrigerant inside your heat pump has reached a higher pressure than the manufacturer expects during normal operation. This can happen during periods of heavy demand or because of restricted airflow, blocked filters, or another component that’s preventing heat from leaving the system efficiently. If a heat pump is under high pressure, it may cycle on and off more frequently, become noisier than usual, or struggle to maintain a consistent temperature throughout your home. In some cases, the unit may temporarily reduce its performance while it protects itself.
The system may continue operating, but the underlying issue will need to be investigated before it develops further.
E3 – Low Pressure
A low pressure error usually means that the refrigerant circuit isn’t operating within its normal range. Refrigerant leaks are a common cause, although very low outdoor temperatures or faults within the system can also trigger this code. Many homeowners first notice that their heating feels less effective or that their heat pump seems to stay on for much longer than usual. Your hot water recovery may also become slower, especially during colder weather.
Continued operation may reduce your heat pump’s efficiency and place extra demand on key components.
DF – Defrost Fault
Heat pumps regularly enter a defrost cycle during cold weather to clear frost and ice from the outdoor unit. A DF error means that this process hasn’t been completed as expected, which prevents the system from returning to normal operation. You may see ice remaining on the outdoor unit for longer than usual, or notice that your heating performance drops while the heat pump attempts to complete the cycle. Cold weather can occasionally trigger a temporary fault, although repeated DF errors deserve attention.
It’s always a good idea to get this looked at early, especially if the code continues to appear or the outdoor unit remains covered in ice.
F3/E4 – Fan Motor Fault
The outdoor fan plays an essential role in moving air across the heat exchanger. If the fan slows down, stops completely or can’t communicate with the control system, your heat pump may display an F3 or E4 error. Poor airflow, unusual rattling noises or a complete loss of heating are all common signs that accompany this fault. You may also notice that the outdoor fan isn’t turning while the system is trying to operate.
Stop using your heat pump and contact a qualified engineer, as continued operation of your heat pump could place additional strain on other components.
H3: E5 – Temperature Sensor Error
Your heat pump uses multiple temperature sensors to regulate its heating and hot water production. An E5 code usually means that one of those sensors is sending unexpected readings, or has stopped communicating correctly. The symptoms can vary depending on exactly which sensor is affected. Some homeowners notice rooms that feel cooler than expected, while others experience inconsistent hot water temperatures or heating that switches on and off at unusual times.
The system may continue operating, although inaccurate readings can affect its overall performance.
H3: E6 – Communication Error
Modern heat pumps rely on constant communication between the outdoor unit, indoor controls and electronic components. An E6 code appears when part of that communication is interrupted. Your controller may become unresponsive, or scheduled heating may fail to start. The system may even restart unexpectedly. Possible causes include power interruptions, wiring faults and temporary electronic glitches.
It’s best to get an engineer to take a look, especially if the code remains after a restart or continues to return.
E7 – Compressor Fault
The compressor performs one of the most important jobs within the entire system, by circulating refrigerant through the heat pump. An E7 code usually points to a fault that requires professional diagnosis. You may notice loud humming noises, poor heating performance, repeated shutdowns or a complete loss of heating and hot water. It’s one that you’ll need to get looked at as soon as you can, since the compressor is such a critical component.
Stop using your heat pump and contact a qualified engineer as soon as possible.
E8 – Water Flow Fault
An E8 error means that water isn’t circulating through your heating system as your heat pump expects. Air trapped in the system, closed valves, blocked filters or a pump issue can all reduce water flow. Many homeowners notice that radiators remain cooler than usual, or their rooms take longer to warm up. The system may also become noisier during operation. The heat pump may also pause while it waits for normal flow to return.
If simple checks don’t resolve the issue or the code keeps returning, get in touch with an engineer.
E9 – Power Supply Issue
An E9 code indicates that your heat pump has detected an interruption or irregularity in its electrical supply. A recent power cut, voltage fluctuation or electrical fault can all trigger this message. The system may fail to start, switch off unexpectedly or restart after the power returns. If the error disappears following a brief interruption and doesn’t return, it’s possible that you might not need to do anything else.
Monitor the system if it resumes normal operation. If the code persists, or continues to reappear, consider booking in with an engineer.
What you should know about error codes and your heat pump’s warranty
An error code doesn’t automatically mean that your warranty is at risk. In many cases, faults that develop during the warranty period are actually covered by the manufacturer’s terms, particularly if they’re linked to a defective component or an issue with the unit itself.
The most important thing is to make sure you respond appropriately. Keeping up with routine servicing, recording any error codes that appear and using a qualified engineer for repairs can all help to demonstrate that your heat pump has been properly maintained. Your owner’s manual and warranty documentation will also explain any requirements that apply to your specific system. And if you’re not sure what your error code means or whether it needs immediate attention, that’s exactly where we can help at ServiceMy.
We specialise in servicing, maintaining and repairing air source heat pumps, so you can rely on experienced engineers who know how to diagnose faults and keep your system performing at its best. Whether you’re looking for the reassurance of a transparent heat pump service plan or need a one-off repair, you’ll receive expert care from a team that’s committed to getting the job done properly.
Just give us a call 0333 050 2091, or explore our heat pump service plans today!
