After giving error code E133 several dozen times over 2 days & repeatedly being reset I too got error code E168 & it refused to be reset anymore... however, when the engineer came out he just removed a small metal 2 pronged pin adjusted the gap between the pins to 4mm, returned it to the boiler, & then left! Now the boiler is behaving nicely again.... Luckily my boiler is my landlord's problem but please note the machine can tell porkies which may cost you dearly if your repair man doesn't check this too!!!!
Relieved to have hot water!!!, July 2010