What does Daikin U1 mean?
Daikin U1 is listed as reverse phase or open phase, open phase, and reversed power-supply phase malfunction in fault lists for more than one model family, including VRV X RXQ-A(N)R cooling only, VRV IV+ REYQ / REMQ heat recovery, VRV 5 Heat Recovery REMA / REYA R32, VRV 5 Heat Pump RYMA / RXYA R32, and ERA-AYF AHU / air curtain. This meaning comes from the manufacturer's own diagnostic material. Do not collapse this code across model families; use the model, series, or system type to choose the right row. Confirm the exact model, series, or signal row before accepting a parts quote.
What to do now
Use these steps to record evidence and match the installed model to its service manual before diagnosis or a repair quote.
Record U1 and match the service manual
Record U1 and stop there; the manufacturer gives no customer reset procedure. Arrange diagnosis with the matching service manual.
No manufacturer reset steps listed for U1
Capture the complete U1 error code and model stickers first. The manufacturer lists the meaning but no customer reset procedure; do not treat a generic power-cycle as manufacturer guidance.
Send these to us
U1 error code, a clear display photo, Daikin indoor and outdoor model stickers, the controller, gateway, or unit that reported the code, operating mode and affected area, and any power or setting changes made after the code appeared
Choose the listing that matches your unit
The same code has more than one listed meaning. Match the model family, the system type and the unit that shows the code before approving parts.
| Code | What it means | What to check first |
|---|---|---|
| Fan Coil | Reverse phase or open phase | Match this meaning to your installed model and the unit that shows the code, then use the checks below. |
| VRV X RXQ-A(N)R cooling only | Open phase | Match this meaning to your installed model and the unit that shows the code, then use the checks below. |
| U1-01 - master / U1-05 - slave 1 / U1-07 - slave 2 / VRV 5 Heat Recovery R32 - U1 / VRV 5 Heat Pump R32 - U1 | Reversed power-supply phase malfunction | Correct the phase order. The alternating U1-01 display belongs to the master outdoor unit. |
| ERA-AYF AHU / air curtain | Reversed power-supply phase (U1-01/04) | Match this meaning to your installed model and the unit that shows the code, then use the checks below. |
- Code
- Fan Coil
- What it means
- Reverse phase or open phase
- What to check first
- Match this meaning to your installed model and the unit that shows the code, then use the checks below.
- Code
- VRV X RXQ-A(N)R cooling only
- What it means
- Open phase
- What to check first
- Match this meaning to your installed model and the unit that shows the code, then use the checks below.
- Code
- U1-01 - master / U1-05 - slave 1 / U1-07 - slave 2 / VRV 5 Heat Recovery R32 - U1 / VRV 5 Heat Pump R32 - U1
- What it means
- Reversed power-supply phase malfunction
- What to check first
- Correct the phase order. The alternating U1-01 display belongs to the master outdoor unit.
- Code
- ERA-AYF AHU / air curtain
- What it means
- Reversed power-supply phase (U1-01/04)
- What to check first
- Match this meaning to your installed model and the unit that shows the code, then use the checks below.
Guidance for your model
Notes that match the code to your exact model. Electrical, refrigerant, wiring, resistance and component checks are for a technician.
| Detail | What it says |
|---|---|
| Singapore / model note | Official Daikin SM-TS3 self-diagnosis row. Manual causes: Power supply reverse phase; T phase open phase; Defective outdoor unit PCB. |
| Singapore / model note | Official Daikin RXQ6-48A(N)R cooling-only service-manual row. Confirm the installed model and matching regional manual before diagnosis; this source is not claimed as universal across every Daikin VRV generation. |
| Singapore / model note | Official Daikin 4PEN561154-1C overview row for REYQ8~20 and REMQ5U7Y1B VRV IV+ heat-recovery systems. The guide refers technicians to the service manual for the complete code list and detailed troubleshooting. |
- Detail
- Singapore / model note
- What it says
- Official Daikin SM-TS3 self-diagnosis row. Manual causes: Power supply reverse phase; T phase open phase; Defective outdoor unit PCB.
- Detail
- Singapore / model note
- What it says
- Official Daikin RXQ6-48A(N)R cooling-only service-manual row. Confirm the installed model and matching regional manual before diagnosis; this source is not claimed as universal across every Daikin VRV generation.
- Detail
- Singapore / model note
- What it says
- Official Daikin 4PEN561154-1C overview row for REYQ8~20 and REMQ5U7Y1B VRV IV+ heat-recovery systems. The guide refers technicians to the service manual for the complete code list and detailed troubleshooting.
What to check before repair
The manufacturer's fault table gives the code's meaning, not a repair procedure. Capture evidence first; model-specific tests belong to the matching service manual.
| You can check | Technician should confirm |
|---|---|
| Photograph the complete U1 error code before taking any action. | Confirm U1 exactly and record which controller, gateway, or unit reported it. |
| Capture the Daikin indoor and outdoor model stickers and identify which controller or unit reported it. | Match the indoor and outdoor model stickers, installed family, and reporting equipment to the source scope. |
| The manufacturer provides no customer reset procedure. Preserve the evidence and use the matching service manual for any system action. | Follow the matching service-manual procedure and keep measured test evidence before naming a failed part. |
- You can check
- Photograph the complete U1 error code before taking any action.
- Technician should confirm
- Confirm U1 exactly and record which controller, gateway, or unit reported it.
- You can check
- Capture the Daikin indoor and outdoor model stickers and identify which controller or unit reported it.
- Technician should confirm
- Match the indoor and outdoor model stickers, installed family, and reporting equipment to the source scope.
- You can check
- The manufacturer provides no customer reset procedure. Preserve the evidence and use the matching service manual for any system action.
- Technician should confirm
- Follow the matching service-manual procedure and keep measured test evidence before naming a failed part.
Source-bounded repair decision
Daikin U1 confirms the fault label the manufacturer lists, not a failed part or repair procedure. Match the installed model to its service manual and require measured diagnostic evidence before approving parts, settings, or refrigerant work.
Whether the reporting controller or unit and exact installed model are confirmed.
What the matching service-manual procedure and measured tests show.
Whether the proposed repair names the evidence for the failed part or condition.
Daikin U1 questions
What does the Daikin U1 error mean?
Can I fix a Daikin U1 error myself?
Is it safe to keep running the aircon with a U1 error?
What causes a Daikin U1 error?
Will a Daikin U1 error need a repair or a full replacement?
What should I send a technician about a Daikin U1 error?
Where to go next
Confirm the fault
Share the error code, model number and symptoms so we can assess the likely cause.
Not the right code?
Browse the full Daikin list or check a few codes in the same fault category.
Read next
Use this quote-check guide only after the matching service manual identifies the diagnostic path.