Do I need a specialist Vokera Engineer?

I have had a Vokera Linea boiler for 4 years, serviced annually by a local Corgi Engineer, it has been "Locking out" regularly, so called the engineer, who serviced and said it would be OK, as it still continued i called him back, and he said I would need an specialist Vokera engineer, would this be normally necessary. I have also been concerned that that it is very noisy and rattles when the hot water is turned on in he bathroom.