A8Worcester Bosch
Worcester Bosch A8: lost communication with the boiler's controls
Checked against Worcester Bosch's own documentation: Worcester Bosch Greenstar CDi Classic ErP user instructions. Last reviewed October 2026. How we check
Engineer only
Worcester describes A8 as a break in communication between the boiler and its FX controls.
What you can safely do
There is nothing you can safely do yourself with this one. Leave the boiler off and book an engineer.
Before you book an engineer
- Write down the code exactly as the display shows it: A8.
- Find your boiler's model name. It is usually on the front panel or in the user manual. The table below shows why it matters: Worcester Bosch codes can mean different things on different models.
- Note when it started and what the boiler was doing (heating, hot water, or starting up).
- If the boiler is still under warranty, check your warranty paperwork before you book anyone.
Call a Gas Safe engineer if
- Contact your installer or a Gas Safe registered engineer to check the controls and wiring.
Find a Gas Safe engineer near you
Opens the official Gas Safe Register search.
Applies to Greenstar CDi Classic. Codes can differ between models, so check your manual.