Get a qualified maintenance guy – I had all the same old problems as everyone else - erratic to fire up and then wasted hundreds of litres of water in the process. Really good hot water when running, though. It was driving us mad. Had one plumber in ages ago and he said - oh that's what you get with Bosch!! So we eventually got in a proper Bosch specialist (from Perth Gas Centre)who appeared to know all the tricks of the trade and was happy to talk about it. He redirected the jets and cleaned, put in a small new part (?), tested flow of water and gas.

It has been running like a dream ever since.

Note they recommend a service every 2 years. He also added that not many standard plumbers are too good on instantaneous hot water heaters - OK, could be sales BS, but you generally know spin when you hear it. He gave us a big tip for Perth conditions - spray with insect / fly spray every 2 months because the little ??? can jam up jets (?) etc. Also, use leave temperature knob around the middle and control temp with the Slider abouve the temp knop. Finally, always run hot and then add cold for best results. Best hot water have ever had from an instantaneous. no "pilot light" so should not blow out. Hassle before we got onto a good service guy