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Daikin heat pump error codes

18 codes that Daikin Europe publishes for its heat pumps, each with what it means, the likely cause, what you can safely check and when to call an installer. Tap your code:

Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work. Anything else is for the heat-pump installer or the maker’s service engineer: in the UK and EU only an F-gas certified technician may open the refrigerant circuit. Codes that need one are marked Installer.

Read this first

Daikin Altherma 3 heat pumps show a fault on the user interface as two characters, a dash and two digits — 7H-01, U4-00, AH-00 — with a warning or error symbol on the home screen. To read it, press the left dial, go to Malfunctioning, and press again for Daikin’s own long description of the fault. The codes here come from the installer reference guide for the Altherma 3 H MT F (EPRA outdoor units with ETVZ indoor units); the owner’s steps come from the operation manual of the Altherma 3 H MT F+W. Models differ: your model’s manual is the authority. Daikin says the problem should be understood and fixed before an error code is reset, by a licensed installer or your dealer.

7H-01 7H-05 Water flow problem

What it means
Too little water is flowing through the heat pump: 7H-01 in general, 7H-05 during heating. Related sub-codes are 7H-04 (hot-water production), 7H-06 (cooling or defrost), 7H-07 (pump deblocking active) and 7H-08 (pump abnormality).
Likely cause
Daikin’s installer guide, for a water flow that is too low, lists: closed shut-off valves, dirty water filters, air in the system, water pressure at or below 1 bar, a broken expansion vessel, or too high a resistance for the pump.
What you can safely check

Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.

  • Read the water pressure on the user interface’s home screen. Daikin asks owners to check regularly that it is above 1 bar.
When to call an installer
Call your installer: the valves, filters, air purge and pump are theirs to check. Tell them the pressure you read.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

AH-00 Tank disinfection not completed

What it means
The domestic hot-water tank’s disinfection (anti-legionella) run did not finish correctly.
Likely cause
The operation manual gives one owner cause: turning tank heating off while disinfection is running causes an AH error. A large hot-water draw during the run can interrupt it too.
What you can safely check

Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.

  • Leave tank heating on while a disinfection run is in progress (the tank screen shows it). Turning tank heating off does not stop disinfection mode, but switching it off mid-run triggers AH.
When to call an installer
If AH returns without that, ask your installer to move the disinfection start to at least 4 hours after your last large hot-water use — Daikin’s own recommendation.

Source: Daikin Europe, Operation manual, Daikin Altherma 3 H MT F+W ETVH/X12, ETBH/X12 (4P634883-2C, 2022.08): 7 Maintenance, 8 Troubleshooting Checked 2026-09-29.

U4-00 Indoor and outdoor unit not communicating

What it means
The indoor unit and the outdoor unit have lost communication.
Likely cause
The communication wiring, power to the outdoor unit, or a circuit board.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

U0-00 Refrigerant shortage

What it means
The outdoor unit has detected a shortage of refrigerant.
Likely cause
Too little refrigerant — usually a leak.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer: only an F-gas certified technician may find a leak and recharge the refrigerant.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

U2-00 Power supply voltage fault

What it means
The outdoor unit has detected a defect in the supply voltage.
Likely cause
An abnormal supply voltage or wiring fault.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

U3-00 Screed dry-out not completed

What it means
The underfloor-heating screed dry-out programme, run to dry a new floor slowly, did not finish correctly.
Likely cause
The dry-out programme was interrupted.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer: the dry-out programme is set and restarted from the installer menus.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

89-02 Heat exchanger freeze-up protection

What it means
Freeze-up protection of the heat exchanger activated during heating or hot-water production (89-01 and 89-03 are the same during defrost).
Likely cause
The water side of the heat exchanger got close to freezing; Daikin’s list gives no further cause for owners.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

80-01 81-00 Water temperature sensor problem

What it means
80-01: the returning-water temperature sensor; 81-00: the leaving-water temperature sensor.
Likely cause
A faulty sensor or its wiring.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

HC-00 Tank temperature sensor problem

What it means
The domestic hot-water tank’s temperature sensor is giving no sensible reading.
Likely cause
A faulty sensor or its wiring.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

HJ-10 Water pressure sensor abnormality

What it means
The water pressure sensor is not working correctly.
Likely cause
A faulty pressure sensor or its wiring.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

AA-01 Backup heater overheated

What it means
The backup heater has overheated, or its power cable is not connected.
Likely cause
An overheated backup heater or a missing power connection.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer: the backup heater and its thermal cut-out are inside the indoor unit.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

E7-00 Outdoor fan motor fault

What it means
The outdoor unit’s fan motor has a malfunction.
Likely cause
A fan motor fault, or something stopping the fan.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

A5-00 High-pressure peak cut or freeze protection

What it means
An outdoor-unit protection: the high-pressure peak cut or the freeze protection has operated.
Likely cause
A pressure or temperature outside the unit’s limits in the refrigerant circuit.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

E1-00 Outdoor circuit board defect

What it means
The outdoor unit’s circuit board is defective.
Likely cause
A board fault.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

U8-02 U8-03 Room thermostat connection lost

What it means
U8-02: the connection with the room thermostat was lost; U8-03: there is no connection with it.
Likely cause
The room thermostat’s link (wiring, or the wireless receiver) to the heat pump.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Contact your installer.

Source: Daikin Europe, Installer reference guide, Daikin Altherma 3 H MT F EPRA08-12EAV3/W1 + ETVZ12E6V/9W (4P634887-1, 2021.03): 14.4 Solving problems based on error codes Checked 2026-09-29.

A code that is not listed here

Daikin’s installer guide lists over 100 error codes, many of them sub-codes of one fault (7H-01 to 7H-08 are all water-flow problems). For a code not listed here, look at the long description under Malfunctioning, then contact your installer: the operation manual shows where to find their contact number (Information › Dealer information). If the heat pump has failed, the backup heater can take over heating and hot water, automatically or after you confirm it on the Malfunctioning screen — at a considerably higher electricity use.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Related pages

Source

Every code on this page comes from these pages, published by Daikin Europe and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.