Following is the fault code table from the Vaillant installation and servicing manual.
8.1.3 Fault codes.
Fault codes take priority over all other display functions in the event of a system fault occurring. If multiple faults occur, the corresponding fault codes are displayed alternately for about two seconds each.
8.1.4 Fault memory
The fault memory stores details of the ten most recent faults.
• Press the ”i” and ”–” buttons simultaneously.
• Use the ”+” button to scroll back through the list of memorised errors. To cancel fault error memory display mode, proceed as follows:
• Press the ”i” button below the display or
• Do not touch any key for about four minutes. The display will now revert back to showing the current flow temperature.