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Worcester Bosch Greenstar 4000 Combi fault 251

System fault boiler electronics / basic controller

Gas boiler

What it means

Fault category V. System fault boiler electronics / basic controller.

Likely causes

  1. Software/electronics fault
  2. Loose wiring on board
  3. Annual service overdue and not reset by engineer

Where to start

  1. Check the electrical connections on the board (check for loose wires etc.)
  2. Navigate to Function check > Activate test
  3. Wait 10 seconds for full component list to display

The full answer, free

  • 3 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 74), 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 Combi. Check the model on the data plate before you order parts.

Other Worcester Bosch Greenstar 4000 Combi fault codes