my worcester 240 combi rsf boiler makes a clatter noise ?

when firing up with the hot water and sometimes the heating, we have to keep resetting it to get the heating and the water back on.
We have changed the main pcb board and the ignition board
Annie, June 2016


done
About 10 - 15 mins after turning the boiler on. It starts making a noise and juddering. Any ideas what it could be and how it can be solved.

Denise, August 2016
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