Worcester Bosch · Greenstar Si Compact ErP
A8 323EMS communication error
This code applies to Greenstar 25Si Compact ErP, Greenstar 30Si Compact ErP. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Power-cycle or reset once only if the user manual specifically permits it.
- If the message remains, arrange an engineer.
How an engineer may fix it
Check configuration, coding, communication buses, plugs, wiring, power supply and control boards; configure, repair or replace the failed control component.
Manufacturer source: Worcester Bosch — Greenstar Si Compact ErP Installation, Commissioning and Servicing Instructions (6 720 813 278). Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.