Daikin Chiller

Daikin Chiller Error Code U8

Troubleshooting guide for the Daikin Chiller system fault U8.

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What It Means

Reports a communication failure specifically between two or more remote controllers wired to the same indoor/chiller control group — for example between a main controller and a sub controller — rather than between a remote controller and the indoor unit itself, which is covered by U5.

Possible Causes

  • Damaged or disconnected wiring between main and sub remote controllers.
  • Both controllers set to 'main' instead of one main and one sub.
  • Loose terminal connections at the remote controller.
  • Defective remote controller PCB.
  • Transmission wiring routed near a noise source.

Not sure which one it is — or if it's none of these? Try ACLogics today.

Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis

Reports a communication failure specifically between two or more remote controllers wired to the same indoor/chiller control group — for example between a main controller and a sub controller — rather than between a remote controller and the indoor unit itself, which is covered by U5. It also differs from U6, which reports lost communication between indoor units rather than between controllers. Check controller wiring and the main/sub controller switch settings, since two controllers both set to 'main' will also produce this fault.

All Recorded Causes

Damaged or disconnected wiring between main and sub remote controllers. Both controllers set to 'main' instead of one main and one sub. Loose terminal connections at the remote controller. Defective remote controller PCB. Transmission wiring routed near a noise source. Incorrect controller address setting.

Verify Before Replacing Parts

  1. Confirm the exact Daikin model family and chiller context before acting on a generic code description.
  2. Confirm board LEDs, wiring polarity, and model compatibility before replacing control boards — this Daikin fault points at damaged or disconnected wiring between main and sub remote controllers.
  3. Check for intermittent communication faults caused by connectors, moisture, or damaged harnesses, and rule out both controllers set to 'main' instead of one main and one sub.
  4. After the correction, run the system long enough to confirm the chiller fault does not return under normal load.

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