Daikin A1-01 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin A1-01 fault code mean?
The A1-01 fault code on a Daikin heat pump points to a failure of the indoor unit's main control board (PCB). Specifically, the microcomputer on that board has stopped responding correctly, preventing the indoor unit from operating. The system will lock out until the fault is cleared, which in most cases means the PCB needs professional diagnosis and likely replacement.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Defective indoor unit PCB Common
The control board itself has developed an internal fault — either through a manufacturing defect, component degradation over time, or physical damage such as moisture ingress or overheating. This is the most common root cause when the A1-01 code appears and does not clear after a full power reset.
- Power surge or voltage spike Common
A sudden surge through the mains supply can stress or permanently damage the microcomputer and supporting components on the PCB. This type of failure often appears immediately after a storm, a grid disturbance, or work carried out on the local electrical supply.
- Electrical noise interfering with the microcomputer Sometimes
High-frequency interference from other electrical equipment on the same circuit, or from poor earthing, can cause the PCB's microcomputer to lose its logic state and trigger an A1-01 alarm. In some cases this is intermittent and a full reset resolves it temporarily.
- Loose or corroded wiring connections to the PCB Sometimes
Vibration over time, or moisture ingress at connectors, can cause intermittent contact between the PCB and other components. This can mimic a board failure and should be checked by an engineer before a PCB is condemned.
How to fix it
- Switch the unit off at the wall isolator or dedicated circuit breaker — not just from the controller — and leave it fully de-energised for at least 60 seconds. DIY safe
A complete power cycle clears any temporary logic fault in the microcomputer. Do not simply put the system into standby from the remote or thermostat; the isolator must be physically switched off. After 60 seconds, restore power and observe whether the fault returns.
- Check your consumer unit for any tripped MCB on the heat pump's dedicated circuit. DIY safe
A tripped breaker can cause irregular power to the PCB and generate spurious fault codes. Reset any tripped breaker once. If it trips again immediately, do not reset it a second time — contact an electrician.
- If the A1-01 code clears after the reset, monitor the unit through one full heating cycle before assuming the problem has resolved. DIY safe
Electrical noise or a marginal connection can cause the fault to return within minutes or hours. If it reappears, the board requires professional inspection rather than repeated resets, which will not fix an underlying hardware fault.
- If the fault persists after a reset, contact an MCS-certified heat pump engineer to carry out board-level diagnostics on the indoor unit PCB. heat pump engineer
An engineer will use Daikin's service software and test equipment to confirm whether the PCB has failed, whether a wiring fault is the root cause, or whether electrical noise is being introduced from elsewhere in the installation. Do not attempt to open the indoor unit or probe any electrical connections yourself.
- If diagnostics confirm the PCB has failed, arrange for the board to be replaced by the engineer. heat pump engineer
Daikin Altherma and other heat pump PCBs are unit-specific and must be correctly configured after fitting. Engineers familiar with Daikin systems can often source the board and complete the replacement in a single visit. Before authorising the repair, check whether your unit is still within Daikin's manufacturer warranty (typically three years for residential units where annual servicing has been maintained), as this may cover the part cost.
Parts you may need
- Daikin indoor unit main PCB (model-specific) · from £280
- PCB wiring harness / connector loom · from £45
- Surge protection device (for future prevention) · from £55
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £450–£900, depending on the underlying cause.
Frequently asked questions
Can I fix a Daikin A1-01 fault myself?
The only step a homeowner can safely take is a full power reset via the wall isolator. If that clears the fault and it does not return, you may not need an engineer. However, if the code comes back — or never clears — the PCB requires professional diagnosis. Opening the indoor unit and working on the control board is not a DIY task: it involves mains-voltage components and proprietary Daikin firmware configuration that requires specialist tools.
How much does it cost to fix a Daikin A1-01 fault in the UK?
For most homeowners, the repair involves an engineer call-out, diagnostics, and PCB replacement, which typically comes to between £450 and £900 including parts and labour. The wide range reflects differences in model, PCB availability, and regional labour rates. If your unit is relatively old and the system has other wear, your engineer may discuss whether replacement of the whole indoor unit is more cost-effective than a like-for-like board swap.
Is my Daikin heat pump still under warranty if it shows A1-01?
Daikin's standard residential warranty covers manufacturer defects for three years from installation, provided the unit has been serviced annually by an F-Gas registered engineer and was installed by an MCS-certified installer. If those conditions are met and the PCB has failed through no external cause, the repair may be covered. Check your installation paperwork and contact your installer or Daikin UK directly before commissioning a paid repair.
Why does my Daikin show A1-01 after a power cut?
A sudden loss and restoration of mains power can cause a voltage spike that upsets or permanently damages the indoor PCB's microcomputer. In many cases a full power cycle after the supply is restored will clear the alarm. If the A1-01 persists, the surge may have caused lasting damage to the board. Fitting a surge protection device on the heat pump's dedicated circuit is a sensible precaution to avoid a repeat.