U2 - The power supply is out of range or has a phase problem.
Daikin's installer guide says U2 points to voltage imbalance or, on three-phase power supply units, a missing phase.
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 startup when power supply conditions are abnormal.
Support first?
Often not
Models in range
FNA25A2VEB, FNA35A2VEB, FNA50A2VEB
What to do first
Start with these checks
- 1Turn the system off.
- 2Do not continue operating until the supply has been checked.
- 3Ask a qualified installer or electrician to inspect the wiring and phase balance.
Likely causes
What usually sits behind this code
Voltage imbalance
Missing phase on a three-phase power supply unit
Power wiring issue affecting correct supply
Contact support
Contact customer support if any of these apply
- !The code appears at startup or after power work.
- !The unit is a three-phase model.
- !Other electrical issues are present at the site.
- - The Daikin guide says operation will be impossible if a phase is missing.
- - For three-phase units, the guide specifically says to recheck wiring and swap two of the three electrical wires if needed.
Related codes
Nearby codes in this family
Source notes
Source and scope
Source: Daikin Installer Reference Guide
Official FNA-A/FNA-A9 guidance links U2 to voltage imbalance or a missing phase on three-phase units.
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.