A heat pump error code is the system telling you, in shorthand, which part of itself has stopped working as expected. It’s a letter-and-number combination shown on the display or app that you look up against your system’s manual to work out whether it’s something you can check yourself or something that needs an engineer. Unlike an old boiler that might just quietly stop firing, a modern heat pump is constantly monitoring pressures, temperatures, flow rates and electrical signals, and it’s designed to tell you the moment something falls outside its normal range.
Why does my heat pump show error codes?
Heat pumps show error codes because they’re constantly monitoring dozens of data points in real time (refrigerant pressure, temperatures, flow rates and electrical signals) and are built to flag anything that falls outside its normal range the moment it happens. If you’ve come from an older gas boiler, this amount of diagnostic information can feel like overkill, but it isn’t: a heat pump is a more complex piece of engineering than a combustion boiler, managing a refrigerant circuit, a compressor, multiple sensors, a circulation pump, and (on air source systems) a defrost cycle, all coordinated by onboard electronics.
That’s actually good news for you as a homeowner. Rather than a system just silently underperforming for weeks while your bills creep up, a fault code gives you an early, specific signal that something needs attention, often before it becomes a bigger problem or a total breakdown. The trade-off is that you’ll now occasionally see codes that look intimidating on a small screen, and it helps to know roughly what you’re looking at.
Where can I find out what my heat pump error code means?
You’ll find out what your specific code means from sources tied to your own system, not a general online list: your manual, your installer’s documentation, the manufacturer’s app, or the manufacturer’s support line. That’s worth saying plainly because there is no single universal list of heat pump error codes: every manufacturer, and often every model range within a manufacturer, uses its own numbering system, and a code that means a minor sensor glitch on one brand’s system can mean something completely different on another’s. So before you do anything else with a code, go to the source that actually applies to your unit:
- Your installation and user manual: most manufacturers include a fault code table near the back, often with a short description and a recommended first action.
- Your installer’s own documentation or handover pack: many installers, HomeKOG included, leave you with a simplified quick-reference sheet alongside the full manual.
- The manufacturer’s app or online portal: most modern heat pumps pair with a smartphone app or web dashboard, and increasingly the fault doesn’t just show as a raw code on the unit; the app translates it into plain language, sometimes with a suggested step or a direct link to book a service call.
- The manufacturer’s website or support line: useful if you’ve mislaid the paperwork, as most brands publish fault code guidance for registered products.
The single most useful habit here is simply keeping your model and serial number somewhere accessible (a photo on your phone, a note on the fridge, whatever works) so that whichever route you use to look up a code, you’re not hunting for it at the same time as dealing with a cold house.
Will my heat pump just show a raw code, or explain the fault in plain English?
On newer systems, “error code” doesn’t always mean a cryptic string of characters. Many current heat pump controllers and companion apps now show a named fault category or a short plain-English description alongside, or instead of, the raw code, and some will even estimate severity (for example, distinguishing a fault that’s stopped the system entirely from one that’s just reduced performance). If your system has an app, that’s usually the fastest way to get useful context, and it’s often what an engineer will ask you to check first over the phone.
What do the different heat pump error code categories generally mean?
Heat pump error codes generally fall into six categories (pressure/refrigerant, sensor, communication/wiring, flow, defrost, and power supply faults), each pointing to a different part of the system. While the exact code will always be brand-specific, the underlying fault categories are broadly consistent across the industry, because every heat pump is monitoring the same basic things: refrigerant pressure, sensor readings, communication between components, water flow, defrost performance, and power supply. Knowing which category a code falls into gives you a useful starting point even before you’ve looked up the exact reference.
| Category | Typical symptom | What it generally means | Homeowner-safe first step | When to call an engineer |
|---|---|---|---|---|
| Pressure/refrigerant fault | System shuts down or won’t start; error on refrigerant circuit | Pressure in the refrigerant circuit is outside normal range. Could be low charge, a blockage, or a sensor misreading pressure | Note the code and any recent weather extremes; do not attempt to access the refrigerant circuit | Always. Refrigerant work is legally restricted (see below) |
| Sensor fault | Odd temperature readings, inconsistent heating, intermittent shutdowns | A temperature or pressure sensor is reading incorrectly, has failed, or has a loose/damaged connection | Check nothing is physically obstructing or has been knocked near the outdoor unit or cylinder sensors | If the fault recurs after a power cycle, or heating performance is clearly affected |
| Communication/wiring fault | Display shows a comms error; indoor and outdoor units seem out of sync | The indoor and outdoor units, or a control module, aren’t talking to each other properly, often a wiring, connector, or signal issue | Check the app or display for connectivity status; check nothing has disturbed a cable run since installation | If it doesn’t clear itself or recurs. This is a wiring-level issue, not DIY |
| Flow/ fault | Reduced heat output, unusual noise from the pump, low flow warning | Water isn’t circulating through the system at the expected rate. Could be air in the system, a closed valve, a struggling circulation pump, or a partially blocked filter | Check that all system valves are fully open and nothing has been shut off (e.g. after other work in the house) | If valves are open and the fault persists. May need bleeding, a filter check, or pump inspection |
| Defrost fault | Ice visible on the outdoor unit that isn’t clearing; reduced output in cold weather | The automatic defrost cycle (air source units) hasn’t completed properly, often during prolonged cold, damp conditions | Check the outdoor unit has clear airflow and isn’t boxed in, covered, or blocked by snow/leaves | If ice builds up repeatedly or doesn’t clear within a normal cycle |
| Power supply fault | System won’t start at all, or trips out intermittently | An issue with incoming power, a tripped breaker, or an internal electrical fault | Check your home’s isolator switch and consumer unit/fuse box for a tripped breaker | If power is confirmed present at the property but the unit still won’t start |
These categories aren’t exhaustive and manufacturers sometimes split them further, but almost every code you’ll encounter maps onto one of these areas. The useful thing to take from this isn’t the code itself. It’s whether the category is one you can safely poke at (power, valves, airflow, obvious obstructions) or one that’s strictly an engineer’s job (anything involving refrigerant, internal wiring, or components inside the unit’s casing).
What should I check myself before calling an engineer about an error code?
Before calling anyone, check five things yourself: the exact code, your power supply, the app or display, obvious physical causes, and whether a manufacturer-specified reset applies. These are worth checking yourself because they resolve a genuine share of call-outs and cost you nothing:
- Write down the exact code before you touch anything. If you reset the system first, you may lose the fault history that would have told an engineer exactly what happened.
- Check the property’s power supply. Confirm the isolator switch (usually near the outdoor unit or in the plant room) is in the “on” position, and check your consumer unit for a tripped breaker or blown fuse.
- Check the app or display for more context. Many systems will tell you whether a fault is active or has cleared itself, and some give a specific recommended action.
- Check obvious physical causes. Is the outdoor unit blocked by snow, leaves, or something stored against it? Are all the system valves open? Has anyone else in the house been doing work nearby recently?
- Follow a manufacturer-specified reset only if your documentation explicitly describes one for that code. Some codes are designed to clear with a simple power cycle; others are not, and forcing a reset on those just hides the underlying problem.
What should you never do when your heat pump shows an error code?
You should never keep resetting a recurring fault and carrying on as normal, touch the refrigerant circuit yourself, ignore a code because the system still seems to work, or remove covers to access internal components. These are the behaviours that turn a manageable fault into a bigger, more expensive, or unsafe one:
- Don’t repeatedly reset a recurring code and carry on as normal. If the same fault keeps coming back, resetting it over and over doesn’t fix anything. It just delays the moment you deal with the actual cause, and in the meantime the system may be running inefficiently or placing extra strain on a failing component.
- Don’t attempt any work on the refrigerant circuit yourself. This isn’t just a safety recommendation. It’s a legal one. Under F-Gas regulations, anyone working on a system’s refrigerant circuit (including checking or topping up refrigerant charge) must hold the appropriate F-Gas certification. Opening the refrigerant circuit without it is illegal, regardless of how confident you feel.
- Don’t ignore a code just because the system “seems to still be working.” Reduced performance often means reduced efficiency, which shows up on your running costs before it shows up as a full breakdown.
- Don’t remove covers or access internal electrical components. Leave anything behind a panel to a qualified engineer.
What information should I give an engineer when reporting a heat pump fault?
Give the engineer the exact code, when it happens, recent weather conditions, anything that’s changed recently, and whether the fault has cleared or keeps recurring. The quality of this information makes a real difference to how quickly the fault gets diagnosed, sometimes even letting an engineer arrive with the right part already in hand. Try to capture:
| Category | Typical symptom | Likely cause | Next step |
|---|---|---|---|
| Pressure/refrigerant | Unit stops, no heat output | Low refrigerant charge, blocked circuit, or faulty pressure sensor | Book an F-Gas certified engineer. Do not open the circuit yourself |
| Sensor | Erratic temperatures, intermittent faults | Failed or disconnected sensor | Report the code; engineer will test and likely replace the sensor |
| Communication/wiring | Units not syncing, display errors | Loose connector, damaged cable, or faulty control board | Report when it started and whether anything disturbed the wiring; book an engineer |
| Flow | Weak heat output, pump noise | Air in system, closed valve, blocked filter, or failing pump | Confirm valves are open, then book a service visit if it persists |
| Defrost | Ice on outdoor unit | Restricted airflow or defrost cycle malfunction | Clear obstructions; book an engineer if ice keeps returning |
| Power supply | Won’t start, random trips | Tripped breaker, wiring fault, or internal electrical issue | Check consumer unit; book an engineer if power is confirmed present |
- The exact code: letters and numbers, written down or photographed from the display.
- When it happens: constantly, only at start-up, only overnight, only during heavy demand (like a hot water reheat).
- Weather conditions: particularly relevant for air source systems, since defrost and pressure faults are often more common in cold, damp, or rapidly changing weather.
- Anything that changed recently: other trades working in the house, a power cut, a change to thermostat settings, or any DIY near the unit or pipework.
- Whether it’s cleared itself or keeps recurring: a one-off code after a power cut is very different from a code that returns every few hours.
The clearer this information is, the less time gets spent on-site simply reproducing the problem, and the more time goes into actually fixing it.
How do I keep a simple heat pump fault log?
Keep a simple heat pump fault log with just a notes app entry or a page in a kitchen drawer notebook. Nothing sophisticated is needed. Every time a code appears, jot down the date, the code, roughly what the weather was doing, and whether it cleared on its own or needed a reset. Over a few months, this turns into useful evidence: an engineer looking at “E4 appeared three times in January, always on very cold mornings” is starting from a far stronger position than one looking at a single isolated report.
It’s also worth keeping the basics to hand at all times, ideally somewhere the whole household knows to find them:
- Your heat pump’s exact model number and serial number.
- The location of the physical manual, or a saved PDF copy.
- Login details for the manufacturer’s app, if it has one.
- Your installer’s contact details and any warranty or service plan reference number.
None of this prevents faults from happening. Sensors fail, connectors work loose, and refrigerant systems occasionally need attention regardless of how well a system was installed. But knowing what a code category generally means, checking the safe things yourself first, and giving an engineer clear, specific information when you do call, consistently gets heat pumps back to normal running faster and with less guesswork on-site.
