Heat pumps fault codes by brand
Find your manufacturer below, then your code. Before you do, know that almost no heat pump code is a job for you — these tables are written for engineers. What is yours is the layer around them: power, water pressure, airflow, condensate, and knowing which alarming-looking behaviour is the machine working properly.
Brands
Pick your manufacturer to see every code we cover.
Most looked-up heat pump codes
Across every brand in this category.
- F.22VaillantWater pressure too low. Vaillant publish exact thresholds and two instructions: the indoor unit manual says inform your competent person; Vaillant UK’s fault page lets a competent owner top up to 1 to 1.5 bar.Get it checked
- Bill has jumpedDaikinThe most important heat pump fault has no code. If your electricity cost has stepped up with no change in habits, the backup heater is probably doing the work.Get it checked
- Vapour from the outdoor unitVaillantA cloud rising off the outdoor unit is the defrost cycle. Vaillant’s own wording is that you do not have to do anything.Usually simple to fix
- U1Mitsubishi ElectricHigh pressure: the outdoor unit’s 63H pressure switch has tripped, at 4.15 MPa on R410A and R32 Ecodans and 3.2 MPa on the R290 range. Mitsubishi say it is usually water flow.Get it checked
- Ice on the outdoor unitDaikinNormal in cold damp weather, and the unit clears it itself. Daikin specifically forbid helping — no hot water, no de-icer, no scraping.Get it checked
- L9Mitsubishi ElectricLow flow on the primary circuit. Formally an installer job, but the causes are things you can often see — a dirty filter, a closed valve, air after radiator work.Get it checked
- Running all the timeVaillantA heat pump is meant to run long and low. The alarm signal is not the running time, it is the bill — and turning the thermostat up will not warm the house faster.Usually simple to fix
- F.511VaillantThe sensoCOMFORT controller has lost contact with the heat pump control module. Vaillant give two causes, a defective cable or a plug connection, and the house may stay warm while it shows.Get it checked
- No code and nothing happeningMitsubishi ElectricMitsubishi resolve four in five support calls on the phone, and publish the four common issues behind them. Three take two minutes and none of them is a code.Get it checked
- 7HDaikinA water flow problem. The sub-code matters more than the code: 7H-01 clears itself, 7H-04 to 7H-06 need a manual reset, 7H-08 is the pump, and 7H-07 is the unit freeing a stuck pump.Get it checked
- EFMitsubishi ElectricA code Mitsubishi define as "non defined": noise on the wiring between the controller, the FTC and the outdoor unit. Their published remedy is to power the Ecodan down for thirty seconds.Get it checked
- Water at the tap is too coldDaikinDaikin give two causes and a remedy that costs money. Before using it, check what your schedule is actually asking the cylinder to do.Get it checked
- Sterilisation cycleVaillantVaillant call it the anti-legionella function: the cylinder is driven above 60 °C on set days, usually at 4 a.m., by the electric back-up heater. It looks like a fault and is not one.Usually simple to fix
- F.532VaillantBuilding circuit flow rate too low, on the earlier aroTHERM monobloc. Vaillant list pressure, blockages, a dirty filter, balancing and air as causes, and send this one to your installer first rather than to Vaillant.Get it checked
- Outdoor unit failureMitsubishi ElectricAny code starting U, F or A means the outdoor unit; Mitsubishi publish that rule themselves. It is the refrigerant side: F-Gas work on R410A and R32 Ecodans, trained-installer work on the R290 range.Get it checked
- L3Mitsubishi ElectricCirculation water temperature overheat protection. The flow rate has probably dropped, and Mitsubishi list three things to check: a water leak, a blocked strainer and the pump.Get it checked
- Radio communication interruptedVaillantA message from the wireless sensoCOMFORT VRC 720f, not from the heat pump. Vaillant’s first instruction is to make sure the power supply is on; the second concerns reception strength.Get it checked
- U0DaikinShortage of refrigerant in the Altherma outdoor unit. Daikin’s own checklist ends with a leak test, the circuit is sealed, and on an R32 unit this is F-Gas certified work by law.Get it checked
- U4DaikinIndoor/outdoor unit communication problem. Daikin’s checks start with the power supply and the wiring between the two boards, and the published reset is a power reset at the outdoor unit.Get it checked
- Protective zoneVaillantaroTHERM plus runs on propane. Vaillant define a zone around the outdoor unit where you may not add sockets, lights, vents or openings — and the duty is yours.Stop — call an engineer
Symptoms
No code on the display? Start from what it is doing.
Heat pump heating the cylinder much hotter than usual
A cylinder that is suddenly at 60 °C or more, usually in the small hours and usually once a week, is the anti-legionella cycle doing its job. Here is how to tell it from a fault.Heat pump not heating the house
Most complaints about a cold house on a heat pump are about how it is being run rather than about a fault, and the giveaway is whether it is running long and steady or short and often.Heat pump not making hot water
A heat pump heats a cylinder rather than heating water on demand, so the questions are how much is in it, how warm it is set and what refilled it.
How heat pumps fault codes work
Read this before you look up a code, because on this category the code is usually not the useful part.
Heat pump fault tables are written for installers, and manufacturers say so. Daikin state plainly that resetting an error code "should be done by a licensed installer or by your local dealer". Panasonic answer nearly every one of their fifty-four published codes with "contact your installer". That is not manufacturers being cautious for the sake of it. A heat pump is a sealed refrigerant circuit bolted to a high-current electrical supply and a pressurised water system, and two of those three are legally restricted work in this country.
So the honest structure of this category is a three-way split, and every page here tells you which side of it your code falls on. Some things are genuinely yours: restoring power at the isolator or the consumer unit, clearing snow and leaves away from the outdoor unit, reading the water pressure gauge, clearing a frozen condensate outlet, checking that a schedule or a holiday setting is not simply suppressing the system, changing thermostat batteries. Some things need a competent heating or electrical person: anything inside an electrical enclosure, sensors, pumps, expansion vessels, flow rates, field settings. And some things are off limits to anyone but a refrigerant engineer: anything that opens the refrigerant circuit, which means pressures, charge, leak detection, recovery, the compressor, the expansion valve and the four-way valve. On R410A and R32 units that is F-Gas certification by law; on the newer R290 ranges, which run on propane, it is the manufacturer’s requirement for an engineer trained on flammable refrigerant.
The single most valuable thing on this page is not a code at all. It is that the correct alarm signal on a heat pump is not "it is running a lot" — it is "my bill has jumped". A heat pump is designed to run long and low, and a household that has come from a gas boiler almost always reads that as a fault. What is genuinely wrong is when a fault has quietly handed the work over to the backup immersion heater. Daikin publish the consequence in their own words: when the backup or booster heater takes over the heat load, electricity consumption will be considerably higher. The system keeps the house warm, nothing obviously fails, and the cost of running it doubles. If your bill has jumped and you have not had a code, that is the thing to investigate.
A short list of things that look like faults and are not, all of them published by the manufacturers themselves. A cloud of vapour rising off the outdoor unit is the defrost cycle — Vaillant's own wording is that you do not have to do anything. Frost on the fins in cold damp weather is expected and is cleared automatically, and you should specifically not help: Daikin forbid using any means to accelerate defrosting other than the ones they recommend, so pouring hot water over an R32 or R290 unit is exactly the wrong move. Radiators that feel merely warm rather than hot are weather compensation working correctly, and turning the setpoint up does not heat the house faster. The circulation pump running while nothing is heating is normal, and Panasonic publish it as such. And radiators going briefly cool mid-cycle is the defrost taking its heat from the heating circuit.
Finally, refrigerant, because it now varies in a way that matters to you rather than just to your engineer. Older units use R410A, a fluorinated gas covered by F-Gas certification. Newer ones increasingly use R32, which is mildly flammable, and a growing number — Vaillant's aroTHERM plus among them — use R290, which is propane. Vaillant do not hedge their wording on it: risk of death caused by fire or explosion if there is a leak in the refrigerant circuit. Propane is heavier than air, so it pools at ground level, and that creates a protective zone around the outdoor unit with an owner duty attached that exists nowhere else in your house. No windows, doors, light shafts, cellar entrances or ventilation openings within it, and no ignition sources either — no sockets, light switches, lamps or electrical switches. Vaillant put the obligation on the owner explicitly: you are not permitted to make structural alterations that infringe the protective zone. Putting up an outside light, adding a socket, building a decking box or fitting a trickle vent near the unit can all breach it, and nobody tells you that when the system is handed over.
Guides
Heat pump defrost and sterilisation cycles: not faults
Vapour off the outdoor unit, ice on the fins, a cylinder heating to 65°C at 3am: the cycles a heat pump runs by design, and what each manufacturer publishes.Heat pump faults: what you can check, and who can touch it
Two circuits, two trades. Gauge, isolators and schedule are yours to check; refrigerant is F-Gas work by law. How each code tells you which side it is on.