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Worcester Bosch Greenstar 4000 System fault 306

Flame signal after closing the fuel supply

Gas boiler

What it means

Flame signal detected after fuel supply closed (V category fault).

Likely causes

  1. Faulty gas valve
  2. Faulty electrodes or connecting leads
  3. Faulty appliance electronics
  4. Incorrect gas type
  5. Incorrect gas supply pressure
  6. Faulty flue system
  7. Incorrect gas/air ratio
  8. Faulty seals around the burner, internal flue seals or case seals causing abnormal O2/CO2 readings
  9. Flue system integrity failure
  10. Combustion circuit fault

Where to start

  1. Check the gas valve
  2. Check electrodes and connecting leads
  3. Check the gas type

The full answer, free

  • 30 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 73), 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 Worcester Bosch manual for the Greenstar 4000 System. Check the model on the data plate before you order parts.

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