The Worcester Bosch 40CDi is a German boiler, it is made by Bosch Junkers and rebadged for the UK.
As a volume installer, I can tell you that this is amongst the most reliable boilers you can buy.
Your posting is somewhat vague, I've read it twice and I'm still not sure whether your complaint involves the boiler failing to light at all and you needing to intervene, or you wanting it to force it up to the set temperature because it shuts down before it gets there.
If it is the latter, there are reasons why boiler manufacturers turn the burner off a few degrees bofore the set temperature, and in a boiler with an aluminium heat exchanger like the Bosch this is more relevant.
Giving advice to potential purchasers is all well and good, but I would suggest any potential Bosch customers to step back and wonder if the 'fault' is actually a misunderstanding on the part of the owner. In which case his post and advice are totally unfair. Your call.
If Gripsfive wishes to check his theories out, the manufacturer is open until 8pm tonight. If he had his Worcester boiler installed by an accredited person, he still has at least 5 yrs warranty left too, in the unlikely event that it is faulty.