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Worcester Bosch Greenstar 4000 System fault 2948

No flame signal with low output

Gas boiler

What it means

Burner starts automatically after purging. This can be caused by strong winds.

Likely causes

  1. Strong winds
  2. Incorrect CO2 settings
  3. Flue outlet exposed to excessive wind pressure
  4. Flue integrity issue
  5. Faulty ignition transformer
  6. Incorrect gas type
  7. Incorrect gas supply pressure
  8. Power supply fault
  9. Faulty electrodes/cable
  10. Faulty flue system
  11. Incorrect gas/air ratio
  12. Faulty external gas flow monitor (natural gas)
  13. Faulty burner
  14. Faulty air/gas ratio control valve
  15. Faulty gas valve
  16. Faulty seals around the burner, internal flue seals or case seals causing abnormal O2/CO2 readings
  17. Flue system integrity failure
  18. Combustion circuit fault
  19. Damaged or loose flue joints
  20. Obstructed or damaged flue terminal or terminal guard
  21. Modified flue gas system
  22. Damaged flue pipes or gaskets
  23. Leaking flue joints

Where to start

  1. Check CO2 settings
  2. Check flue outlet position for effects of excessive wind pressure
  3. Check flue integrity

The full answer, free

  • 61 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 76), 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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