Im not sure.
I did one a few months ago and im sure it was rubbish. I cant exactly remember but 2years sticks in my mind. For the cost of the boiler (837 model) very poor indeed
10 yrs on the ecotecplus, 7 on the pro's til the end of the year (I think)
If you're a member of the Vaillant advance scheme
Although I suspect that to keep up with the other manus, they'll keep the extended warranties ongonig