A8
Worcester Bosch
Control Interface / Bus Communication Fault
Boiler shows A8, may not respond correctly to room thermostat or controls.
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Faulty Worcester Bosch EMS/Bus room controller, Incorrect wiring polarity on control bus, Faulty PCB communication circuit
How to Fix / Troubleshooting
Safety first: Isolate power before working on control wiring.
Engineer checks:
- Inspect the low-voltage control bus wiring between the boiler and Worcester Bosch controller (e.g., Wave, EasyControl, Comfort+); ensure correct polarity and secure connections.
- Temporarily disconnect the external controller and fit a link or basic on/off thermostat as per wiring diagram to test boiler operation.
- If boiler operates normally with a basic control, replace the Worcester Bosch controller.
- If fault persists, test and replace the main PCB if communication circuit is defective.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Worcester Bosch EMS Room Controller
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements