Over many years, KWE has built up a substantial knowledge base of faults and how to fix them. We call this our Faultbase. We use this a lot in-house, but readers are welcome to take a look themselves. It is just an Excel spreadsheet, but it could really help owners who are stuck. We have left it as a spreadsheet so that users can apply filters to make it more useful. There is also a .pdf version.
Fault Finding Guide