What it means
On the Greenstar CDi Classic it shows as A8. On Si, CDi and i System Compact ErP boilers it's A8 with 323 under it. On the Greenstar i ErP, A8 with 361 means something different, so check the number under the code.
What to check, in order
- Note the code and the number under it
Worcester asks you to quote both when you call.
- Call a Gas Safe registered engineer
Worcester's CDi Classic manual says not to try to put listed faults right yourself.
When to call a Gas Safe engineer
Worcester gives the cause as the communication link (BUS or EMS) to the programmer being interrupted.
A repair visit will usually check the wiring first, then the boiler's control board.
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Worcester Bosch A8 fault code mean?
The boiler has lost communication with its programmer or room control. On the Greenstar CDi Classic it shows as A8. On Si, CDi and i System Compact ErP boilers it's A8 with 323 under it. On the Greenstar i ErP, A8 with 361 means something different, so check the number under the code.
Can I fix Worcester Bosch A8 myself?
Engineer only (engineer visit). Start with: note the code and the number under it; call a Gas Safe registered engineer. Worcester gives the cause as the communication link (BUS or EMS) to the programmer being interrupted.
Is Worcester Bosch A8 worth repairing?
Get a quote first. It may be a wiring connection or the control itself. Ask for a price before agreeing to new parts.
Checked against
- Worcester Bosch Greenstar CDi Classic engineer's service booklet (PDF)
- Worcester Bosch Greenstar Si Compact ErP installation and servicing instructions (PDF)
- Worcester Bosch Greenstar i user instructions (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.