A8 checks
| Step | Check | If yes | If no / next |
|---|---|---|---|
| 1 | Wiring between programmer and appliance. Use terminals B only (centre terminal is not for bus). Is there continuity? | If A8 remains, go to step 2. | Correct or replace the bus cable, then power on. |
| 2 | Multiple bus modules: wiring between modules and the branch box on terminals B. Continuity? | If A8 remains, go to step 3. | Repair or replace the cable. |
| 3 | Wiring between branch box and programmer on terminals B. Continuity? | If A8 remains, go to step 4. | Repair or replace the cable. |
| 4 | Has the programmer been replaced? | Go to step 5. | Replace the programmer. |
| 5 | Has the bus module been replaced? | Go to step 6. | Replace the bus module. |
| 6 | PCB control board | Note service settings, replace the PCB, restore settings. |
Gas work stays with a Gas Safe registered engineer. These steps are guidance from the manufacturer sequence, not a substitute for the handbook.