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Viessmann Vitodens 100-W fault 68

Flame signal is already present at burner start

Gas boiler

What it means

Burner enters a fault state because a flame signal is detected before the burner has started, suggesting a false flame signal or faulty ionisation circuit.

Likely causes

  1. Faulty ionisation electrode circuit
  2. HBMU heat management unit fault

Where to start

  1. Close the gas shut-off valve and safeguard against reopening.
  2. Remove connecting cable of the ionisation electrode
  3. Reset the appliance

The full answer, free

  • 11 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 71), right under the answer
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Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.

From the Viessmann manual for the Vitodens 100-W. Check the model on the data plate before you order parts.

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