I found the Boiler Fault Finder very helpful tool. It covers all the aspects of fault finding that any engineer will encounter day to day out there, wiring, tips and faults and so many more.
You can tell that it is designed by engineers who have been on the tools and not by someone who only knows the theory.
I found very useful the top tips for heating engineers section and also anything that Is related to wiring.
One of my struggles out there was the use of the multimeter
, and thanks to this tool it cleared up confusions in regards to thermistors
I really like that you can also download manuals for all the main boilers brands, vaillant, Worcester, Main, Ideal, Baxi, Potterton and many more.
Unlike to many similar tools /apps out here, Boiler Fault Finder is build by engineers f engineers, and focuses on the problems an engineer will come across in a job, providing tips and solutions.
I have recommended to colleagues and they will definitely will give it a go.