You can read the instructions until you are 'blue in the face' and it may not help!
I had one of these boilers fitted when builders made me a new kitchen extension, the plumber was 'subbed' in and handed me the instructions as he left saying that he 'didn't like Ferroli' and to talk to the builders about how to use it!
After months of tripping (mostly on 'A3' fault code), both plumber and builder ignoring all pleas for help (once they have your money, why would they return?!?!?), I figured out a way to keep the trips to a minimum... never run the bath or shower if the central heating is on!
I would strongly recommend that you do not call Ferroli UK... a premium cost line and kept on hold/waiting for what seems an age (a clever way of earning extra cash?!!!). Eventually an operator declares that my boiler is out of warranty because they haven't received the installation paperwork within a month of fitting, so they cannot help. She wasn't interested in who the plumber or builder was either, but was very keen to send a plumber round at a crazy cost, and any work would be at a crazy cost per hour with no guarantee of fixing the problem. She wouldn't allow me to speak to a supervisor so that was it!!!
I've contacted several gas safe engineers/plumbers and two have said they are not interested in trying to fix a Ferroli boiler (but would be happy to quote to replace it!). 3 have had a look/play and not fixed the issue and now I've almost had enough... maybe I should just get it replaced again!?!?
Any gas safe engineers/plumbers with a genuine knowledge and ablility to repair/fix the Ferolli Optimax HE Plus 31C is welcome to contact me through the forum (I may still have a job for you!!)
Sensible suggestions appreciated!