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Worcester Bosch Greenstar 4000 System fault 1010

No communication via EMS BUS connection

Gas boiler

What it means

Loss of communication over the EMS BUS between the boiler PCB and connected room controls/Key devices.

Likely causes

  1. Faulty/disconnected grey ribbon low voltage connection
  2. Incorrect Key connector positions
  3. Key not fully home
  4. Flat room control batteries
  5. Missing bridging links at LR & 230V out
  6. Incorrect EMS BUS voltage
  7. 230V wiring interference alongside BUS connections
  8. Faulty control unit

Where to start

  1. Check the grey ribbon on far right of the PCB (low voltage connection)
  2. If using a Key control product check the Key connections (black, white, red, green) are plugged into the correct position on the PCB
  3. Check that the Key is pushed fully home

The full answer, free

  • 4 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 System. Check the model on the data plate before you order parts.

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