Does boiler have a mode button?
Of it does press and hold for 2 sec and release you can then toggle between heating and hot water to set the temp for each
Most likely the fan as it is the most common cause of blown fuse on fuelsaver as its motor sits in the flueway it was probably running slow and not quite making air pressure switch and when you knocked lhs it triggered air pressure switch. I would not recommend a diy fix as its a positive flued...
Expansion vessel will need recharging with footpump to 1 bar you will need to put a hose on a drain point first and leave it open whilst pumping up expansion vessel