i have same problem from time to time. same boiler. i usually get it if i've drained the central heating side (to add fernox) etc. but then sometimes it just does it.
i think its probably an air lock in the boiler.
turn off boiler take off top lid and open the grey/white bleed screws. then switch boiler on, and turn on a hot tap, and demand heat from central heating by turning up thermostat if you have one. repeat several times.let me know. cheers
disting
May 2008