Daikin heat pump fault codes

Daikin Altherma codes come in two forms depending on how old your controller is, and the difference matters — U4 and U4-00 are the same family, but 7H-01 and 7H-08 are different jobs. Daikin also state plainly that clearing these is a job for your installer rather than for you.

Where the code shows on a Daikin

Daikin print an Altherma code in two parts, an error code and a detailed error code, and the controller shows them together: 7H-01, U4-00, E3-24. The first part is the fault family and the second narrows the cause, so looking up only the first half against an old two-character list will give you the wrong component. The two-part form is in Daikin’s installer guides from at least 2018 and on every Altherma 3 controller; the bare form, U4 or E7 or H3, is what Daikin UK’s own owner leaflet describes as "typically a number and a letter, for example 7H" and what older displays show. Every Altherma 3 controller also tells you the meaning in words: open the main menu with the left dial, go to Malfunctioning, and it gives a short description with the code, then a long one. Two more cues. Where the description begins "OU:", Daikin mean the fault is in the outdoor unit, which in most cases puts it in the refrigerant or inverter side and out of reach of anyone without F-Gas certification. And Daikin’s air conditioners use the same two-character vocabulary, so some codes — U0, U4, A5 — appear in both tables with different systems behind them. If your Daikin is a wall-mounted air conditioner rather than an Altherma with radiators or a cylinder, the pages in our air-conditioning section are the ones for you.

How to reset a Daikin

Daikin’s position is consistent across their documents: the installer reference guide says it is important to understand the problem and take measures before resetting an error code, and that this should be done by a licensed installer or by your local dealer; Daikin UK’s technical support page tells owners who see an error code to contact their certified installer right away. Behind that, the service manual gives every code one of three reset classes, and the pages here quote them. "Automatic reset" codes clear themselves once the condition passes, and Daikin publish 7H-01, 7H-07, 7H-08, 89-02, 89-03, AH-00, C0-01, U0-00 and U5-00 in that class. "Manual reset via user interface" codes stay until someone resets them on the controller, and the installer guide notes that the user interface itself displays how; 7H-04, 7H-05, 7H-06, 89-01, A5-00, C0-00, C0-02, E3-00 and E7-00 are in that class. "Power reset via outdoor unit" codes — U4-00 among them — need the outdoor unit’s supply cycled. Daikin UK’s older owner leaflet for the Altherma LT split does give an owner reset: turn the power off, wait 60 seconds, turn it back on, and if the code returns, note it and call. Two things to establish before treating anything as urgent: whether the home screen shows an error or a malfunction, since Daikin distinguish the two by severity, and whether you actually have heat, since several codes are annotated as warnings and the unit keeps running through them.

Most common Daikin faults

The Daikin codes people look up most.

Every Daikin fault code

13 published codes. Filtering happens in the page — every one is in the HTML.

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Showing 13 of 13 codes

Every published Daikin fault code with its meaning and severity
Code	What it means	Severity
Bill has jumped	The 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
Ice on the outdoor unit	Normal 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
7H	A 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
Water at the tap is too cold	Daikin 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
U0	Shortage 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
U4	Indoor/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
AH	The tank disinfection cycle did not complete: the setpoint was not reached within six hours or not held long enough. The unit keeps running, and Daikin’s first cause is hot water drawn mid-cycle.	Get it checked
E3	The outdoor unit’s high pressure switch has opened. Daikin list a closed stop valve, a faulty sensor or switch, overcharge, moisture, a blockage and the fan, and require a manual reset.	Get it checked
A5	High pressure peak cut in heating, freeze protection in cooling. On an Altherma, Daikin’s first four checks are all water-side: pressure, flow, stop valves and air. Not the indoor filter of an air conditioner.	Get it checked
H4	Malfunction of the low pressure switch, a protection device on the refrigerant side of the outdoor unit. Daikin publish the name and nothing an owner can act on; it is certified work.	Get it checked
C0	Flow sensor malfunction: the sensor sees water moving 45 seconds after Daikin’s pump has stopped. Low pressure, air and an external pump running are on the list before the sensor itself.	Get it checked
89	Heat exchanger frozen. 89-02 and 89-03 are warnings that reset themselves; three of them within half an hour of each other lock the unit out with 89-01, which needs an engineer.	Get it checked
E7	The outdoor unit fan did not start within thirty seconds of being told to. Daikin’s checks are the fan motor and the main PCB; what you can check is whether anything is stopping the blades.	Get it checked

Daikin models

Codes can differ between generations. Check yours.

Guides that help with Daikin faults

Looking for Daikin’s own support? www.daikin.co.uk. We are not affiliated with Daikin.