E6
Viessmann Indoor–Outdoor Communication Error

Indoor unit shows E6; outdoor unit may not respond; no cooling or heating

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Broken communication cable, Reversed communication wiring, Faulty indoor PCB communication circuit, Faulty outdoor PCB communication circuit

How to Fix / Troubleshooting

Safety: Turn off all power before working on wiring.

  • Inspect interconnecting cable: Check the cable between indoor and outdoor units for physical damage.
  • Verify wiring order: Confirm that terminals (e.g., 1–2–3, S, L, N) are wired identically at both ends. Correct any miswiring.
  • Check for shared circuits: Avoid sharing the communication cable with other systems or running it parallel to high-voltage cables where possible.
  • Board diagnosis: If wiring is correct and intact, one of the PCBs may be defective and should be tested and replaced by a technician.
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Repair Difficulty

Hard 4/5

Required Part

Outdoor Main Control PCB
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