The first generation had a grey control fascia. Some of the first production run, 5 years ago could develop a leak in the heat exchanger after a while though these have mostly been dealt with under warranty.
When you say overflow, do you mean a copper pipe (usually) from the boiler to outside and it's dripping from there or do you mean a plastic condensate drain from the boiler?
If the former the earlier answer is possibly correct, if the latter you may have a leak in the heat exchanger which will need to be changed.
Don't think Vokera would do it under warranty as they only had 2 years though you could ask but they do do a fixed price repair for £230 which would cover it.
Bill, July 2015