Daikin UF-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin UF-00 fault code mean?
The UF-00 code indicates that the Daikin system has not been correctly set up or commissioned. Specifically, the heat pump's control system has detected a mismatch between the refrigerant pipework configuration and the transmission wiring linking indoor and outdoor units, or a required commissioning procedure was never completed. In plain terms, the system cannot confirm that it has been installed and set up correctly, so it refuses to run. This is fundamentally an installation or commissioning fault rather than a component failure, although a faulty PCB can produce the same code.
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
- Transmission wiring incorrect or crossed Common
The signal wiring between the indoor and outdoor units (terminals 1, 2 and 3) has been connected in the wrong order or with crossed terminals. Polarity matters on Daikin systems, and even a single transposed wire will prevent the units from communicating correctly, triggering UF-00.
- Mandatory check operation not completed Common
Daikin requires engineers to run a built-in commissioning check via the service menu after any new installation or system modification. If this step was skipped, interrupted or not acknowledged, the system remains in an uncommissioned state and displays UF-00 indefinitely.
- Refrigerant stop valve left closed Common
One or more of the refrigerant stop valves on the outdoor unit were not fully opened after installation. The system cannot circulate refrigerant or pass its internal checks while a valve remains shut, which can result in the UF-00 condition appearing during or after commissioning.
- Piping and address mismatch on multi-zone systems Sometimes
On VRV or multi-split configurations, each indoor unit is assigned a software address that must correspond to its physical refrigerant pipework connection. If the addresses and pipework do not match — perhaps after a system expansion or modification — the controller raises a UF fault.
- Defective indoor unit PCB Rare
Daikin's own service documentation lists a faulty indoor unit printed circuit board as a direct cause of UF-00. If all wiring, valves and commissioning steps have been verified as correct and the fault persists, the PCB may be sending or failing to send the expected signals.
How to fix it
- Switch the unit off at the controller and check for any tripped MCB in the consumer unit DIY safe
Before anything else, confirm the system has power and that no circuit breaker has tripped. Reset any tripped MCB once, then power the heat pump back on. If UF-00 returns immediately, the fault is genuine and requires an engineer — do not keep resetting.
- Check around the outdoor unit for obvious obstructions DIY safe
Clear any leaves, debris or compacted snow from around the outdoor unit casing and ensure airflow is unrestricted. This will not resolve UF-00 on its own, but it is good practice and rules out any secondary issues before an engineer visits.
- Check the system pressure on the heating circuit DIY safe
Look at the pressure gauge on the indoor unit or buffer vessel. It should typically read between 1.0 and 1.5 bar when cold. If it is below 1.0 bar, top up via the filling loop following your system's manual. Low pressure is not the cause of UF-00 but can complicate diagnosis if present alongside it.
- Contact an MCS-certified engineer to inspect the transmission wiring heat pump engineer
An engineer should check that terminals 1, 2 and 3 between the indoor and outdoor units are connected in the correct order and that no wires are crossed or loose. On multi-zone systems, all inter-unit wiring must be verified against the installation diagram. This is not homeowner-safe work as it involves opening electrical enclosures on the units.
- Have the engineer verify all refrigerant stop valves are fully open heat pump engineer
The stop valves on the outdoor unit must be fully open before the system can operate or pass commissioning. An engineer will confirm valve positions as part of a systematic check. Refrigerant circuit access is reserved for F-Gas registered engineers.
- Have the engineer run the Daikin mandatory check operation heat pump engineer
Daikin requires a specific commissioning procedure to be completed via the service menu. An engineer familiar with Daikin systems will access the service mode, initiate the check operation and confirm the system passes. UF-00 will persist until this step has been successfully executed.
- On multi-zone systems, have the engineer verify indoor unit address settings heat pump engineer
The software address assigned to each indoor unit must match its actual position in the refrigerant pipework. An engineer will cross-reference the system's configuration map against the physical installation and correct any mismatches in the service menu.
- If the fault persists after all of the above, arrange indoor PCB testing and replacement heat pump engineer
Where wiring, valves and commissioning have all been confirmed as correct but UF-00 remains, the indoor unit PCB is the likely culprit. A Daikin-trained or MCS-certified engineer should test the board and arrange a replacement if required. This is specialist work.
Parts you may need
- Daikin indoor unit PCB (model-specific) · from £280
- Transmission wiring (2-core or 3-core screened cable, per metre) · from £3
- Refrigerant stop valve (service valve replacement) · from £45
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 £150–£400, depending on the underlying cause.
Frequently asked questions
Can I reset a Daikin UF-00 fault myself?
You can try a full power cycle — turn the unit off at the controller, switch off the isolator and wait two minutes before restoring power. However, UF-00 is a commissioning or wiring fault, not a transient error, so it will almost always return unless the underlying cause has been fixed. Repeated resets without addressing the root cause will not help and could mask a more serious issue. An MCS-certified engineer is needed to properly diagnose and clear this fault.
Is UF-00 covered under Daikin's warranty?
It depends on the root cause. If UF-00 is traced to a faulty indoor PCB that has failed within the warranty period, Daikin's standard warranty (typically three years on residential units for parts) should cover the component, provided the system was installed by a qualified engineer and has been serviced annually by an F-Gas certified engineer. However, if the fault is due to an installation error — crossed wiring or a missed commissioning step — this is unlikely to be covered under warranty, as it reflects incorrect commissioning rather than a manufacturing defect. Keep all service records.
How much does it cost to fix a Daikin UF-00 fault in the UK?
For the most common cause — a wiring correction or a missed check operation — most homeowners pay in the region of £150 to £400, which typically covers an engineer call-out and the time spent re-commissioning the system. If the indoor PCB turns out to be faulty, replacement costs can add £450 to £900 or more depending on the unit. Compressor or major refrigerant circuit repairs, which are rarely the cause of UF-00 specifically, can run to £1,000 or beyond on larger systems.
Why has UF-00 appeared on my Daikin system after years of working fine?
UF-00 is primarily an installation and commissioning code, so seeing it on an established system that has been running without problems is worth investigating carefully. Possible triggers include a recent engineer visit where settings were altered, a power interruption that corrupted the system's configuration, or a developing PCB fault. It is also possible that the code has a slightly different meaning on your specific model — Daikin uses the UF designation across many product lines and the sub-code or context can vary. An engineer with access to Daikin's service documentation for your exact model will be best placed to diagnose it.