Thank you all (so many) for your replies.
A few points, please, I wish to add.
a) Installation was carried to the highest possible standards. This is not our first house or first boiler. Boiler water treatment chemicals were added plus a small cylinder (water purifier?) added to the piping system. Three Corgi engineers, around 6 hours and £900 to install it.
b) Correctly so, customer service from Vaillant is not very good
c) From 1976 to 2004 we have never had such problems with any boiler. Four houses + two flats
d) When in 2008 the old boiler (I mean old as it was in the house when we bought it in 2004) broke down, instead of a £300 repair I felt it was a good idea to have a new, more powerful one instead (now I have the wife nagging and telling me how wrong I was). Do you know how that feels like!?
e) Do you really service your car every year? I don't. It depends on mileage. Last gap has been a two years period as, since 2012, I must have done no more than 4000 miles in my car.
f) I have no personal dispute with Vaillant at the moment. I have made enough comments on Facebook at that time.
g) On count of probabilities, if the boiler was serviced every year and the above was still going wrong, who should we blame this time? (...the wrong type of snow)??? We should only allow British Rail for such "jokes".
h) As it happens boilers are meant to be working with water (no rocket science). I am no boiler engineer but for so many components to go wrong one after the other only indicates to me that there is (was) something drastically wrong with the components or manufacturing to start with.
I am passionate about watches and it has been my hobby for over 50 years. However I will be the first one to state that watches do not need to be serviced every year and that a £5,000 Rolex is no better than a £300 Tissot or Longines. I do not expect anyone to "spit on their plate" and tell me what they really believe is going on with my boiler. My personal experience with Vaillant (and two BMW 5 series) is negative based on personal experience/circumstances. This is why we now drive Audi and Skoda and this is why we will never buy a Vaillant again. Luck should not come into the equation and if this is just the odd one out, Vaillant should have also been more pro-active in providing 'some' and better customer service.