F17
Viessmann Mains Supply Fault

F17 error, unit indicates power supply or frequency issue

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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

Incorrect supply voltage, Unstable mains frequency, Loose power terminal connections, Shared circuits causing interference

How to Fix / Troubleshooting

Safety: Turn off power at the breaker before opening the electrical connection box.

  • Verify supply: Confirm that the heater is connected to the correct voltage and frequency as stated on the rating plate (typically 230 V, 50 Hz in many regions).
  • Check terminals: Remove the electrical cover and inspect the L, N, and PE terminals. Tighten any loose screws and ensure no discoloration or burning.
  • Dedicated circuit: Where possible, connect the heater to a dedicated circuit to avoid interference from large motors or inverters.
  • Surge and power quality: If mains quality is poor, consider installing a power conditioner or consult an electrician.
  • Reset: Restore power and clear the F17 code. If it recurs, the internal power supply on the PCB may be faulty and needs professional replacement.
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Repair Difficulty

Medium 3/5

Required Part

Power Supply Section (Main PCB)
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