F7 checks
| Step | Check | If yes | If no / next |
|---|---|---|---|
| 1 | Electrodes dirty or defective (wear, deposits, mechanical damage)? | Replace the electrode assembly and reset. | Refit electrodes, reset, go to step 2. |
| 2 | CO2 in combustion air above 0.2% with the casing on? | Flue gases in the combustion air — check and repair the flue. | Go to step 3. |
| 3 | PCB damaged | 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.