Daikin UA-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin UA-00 fault code mean?
The UA-00 code on Daikin heat pump systems indicates a system combination or configuration problem — typically that the indoor and outdoor units are not correctly matched, that too many indoor units are connected to a single outdoor unit, or that a replacement PCB has not been properly configured after installation. In some models, UA-00 briefly appears during the initial power-on self-check and clears on its own once the unit confirms everything is in order. If the code disappears within a minute or two and the system runs normally, no action is needed. If it persists, it points to a genuine configuration or hardware fault that requires an engineer.
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
- Mismatched indoor and outdoor units Common
The indoor and outdoor units installed together are not a compatible combination according to Daikin's engineering specifications. This commonly occurs after a partial system replacement where only one part of the system was swapped out, leaving an incompatible pairing in place.
- PCB not reconfigured after replacement Common
When an outdoor unit PCB is replaced with a spare board, Daikin requires the engineer to carry out specific field-setting procedures using service tools. If those settings are skipped or incomplete, the system detects a configuration mismatch and raises UA-00.
- Faulty or defective outdoor unit PCB Sometimes
The outdoor unit PCB itself may have developed a fault, causing it to misreport or fail to recognise the connected indoor unit or units. This can produce a UA-00 even when the physical installation is correct.
- Incorrect transmission wiring between units Sometimes
The communication cabling linking the indoor and outdoor units — or between multiple outdoor units on a multi-system — may be incorrectly connected, reversed, or damaged, preventing the units from correctly identifying one another.
- Too many indoor units connected Sometimes
On multi-split configurations, connecting more indoor units than the outdoor unit is rated to support will trigger this code. This is typically an installation error rather than a fault that develops over time.
- Refrigerant type mismatch Rare
If the indoor and outdoor units are designed for different refrigerant specifications, the system may detect an incompatibility at the configuration level and raise UA-00. This is rare in properly installed systems but can occur after non-like-for-like component replacements.
How to fix it
- Check whether the code clears on its own at start-up DIY safe
On some Daikin models, UA-00 is a normal part of the power-on diagnostic sequence and will disappear within a minute or two once the self-check completes. Watch the display after powering on — if the system moves to a normal operating display and runs without issue, no further action is needed.
- Perform a full power reset DIY safe
Switch the heat pump off at the controller, then turn off the isolator or circuit breaker for the outdoor unit. Leave the system completely de-energised for at least five minutes, then restore power and observe the display. A transient communication glitch can sometimes cause UA-00 and may not return after a clean restart.
- Check for any obvious external issues around the outdoor unit DIY safe
While the unit is powering back up, visually inspect the outdoor unit. Clear any debris, leaves or ice that may have accumulated around the casing. Ensure the unit has adequate clearance on all sides and the fan outlet is unobstructed. Check that no cables are visibly pinched or disconnected at the accessible external connection points.
- Verify system pressure is within range DIY safe
Check the system pressure gauge or the reading on the controller. Normal operating pressure is typically between 1.0 and 2.0 bar when cold. If pressure is low, top up via the filling loop according to your system instructions. Low pressure alone will not usually cause UA-00, but ruling it out is good practice before calling an engineer.
- If the code persists, contact an MCS-certified heat pump engineer heat pump engineer
A persistent UA-00 requires an engineer to inspect the installation. They will verify that the indoor and outdoor units are a compatible combination, check the communication wiring between units, and confirm whether a PCB replacement or reconfiguration is needed. Any work involving the refrigerant circuit, the compressor, PCB replacement or field-setting programming must be carried out by a qualified engineer — refrigerant work specifically requires an F-Gas registered engineer.
Parts you may need
- Outdoor unit PCB (main control board) · from £320
- Communication/transmission wiring harness · from £45
- Indoor unit PCB · from £180
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–£450, depending on the underlying cause.
Frequently asked questions
Is UA-00 always a serious fault on a Daikin heat pump?
Not necessarily. On certain Daikin models, UA-00 appears briefly during the power-on self-check and clears automatically once the unit confirms everything is correctly configured. If the code vanishes within a couple of minutes and the system operates normally afterwards, it is simply part of the start-up routine. However, if UA-00 stays on the display or keeps returning, it indicates a genuine configuration or hardware problem that an engineer needs to investigate.
Can I fix a Daikin UA-00 error myself?
The only steps a homeowner can safely take are a power reset and a visual check around the outdoor unit. The underlying causes of a persistent UA-00 — such as a misconfigured PCB, incompatible unit pairing, or wiring fault — require an MCS-certified heat pump engineer with access to Daikin service tools. If the PCB needs to be replaced, the engineer must also carry out the correct field-setting procedure, which cannot be done without manufacturer software. Attempting to work on the PCB, refrigerant circuit or internal wiring yourself is unsafe and could invalidate your warranty.
How much does it typically cost to fix a Daikin UA-00 fault in the UK?
For the most common causes — wiring correction, PCB reconfiguration or field-setting after a board swap — expect to pay roughly £150 to £450 including the engineer's callout and labour. If the outdoor unit PCB itself has failed and needs replacing, the cost rises considerably, typically £450 to £900 depending on the model and labour rates in your area. Major components such as a compressor can cost significantly more, but this is rarely the direct cause of a UA-00. Always ask your engineer to diagnose the specific cause before authorising any parts.
Will my Daikin warranty cover a UA-00 fault?
It depends on the cause. Daikin's standard residential warranty covers manufacturing defects on parts for three years, but only if the system has been serviced annually by an F-Gas certified engineer and all work has been carried out to the correct standard. If UA-00 is caused by an installation error — such as mismatched units or a PCB that was not properly configured after replacement — this may be covered under the original installer's workmanship warranty rather than Daikin's product warranty. Keep all service records, as Daikin will ask for them before honouring any claim.