U0 - The system sees closed stop valves.
In the official FNA-A/FNA-A9 installer reference guide, U0 is flagged when the stop valves are closed.
Grounded in the official Daikin FNA25~60A2VEB(9) installer reference guide error tables for commissioning and troubleshooting.
Severity
High
Display
Shown on the user interface during test run or fault diagnosis.
Support first?
Often not
Models in range
FNA25A2VEB, FNA35A2VEB, FNA50A2VEB
What to do first
Start with these checks
- 1Stop the unit and avoid repeated restart attempts.
- 2If the system was recently installed, ask the installer to verify the refrigerant stop valves are fully open.
- 3Do not try to force operation until the refrigerant circuit setup is confirmed.
Likely causes
What usually sits behind this code
Liquid or gas stop valve left closed after installation
Refrigerant circuit not opened correctly for operation
Contact support
Contact customer support if any of these apply
- !The unit is newly installed or recently serviced.
- !The code appears immediately after startup.
- !You cannot confirm valve position safely.
- - Daikin's table gives a single direct cause for U0: closed stop valves.
- - This is commonly an installation or commissioning issue.
Related codes
Nearby codes in this family
Source notes
Source and scope
Source: Daikin Installer Reference Guide
Official FNA-A/FNA-A9 guidance lists U0 when stop valves are closed.
Last reviewed: 2026-04-19
Daikin fault handling varies by indoor and outdoor unit combination, refrigerant type, and controller. Confirm the exact model pair and full fault history with an authorised Daikin technician before replacing parts.