IMO Plumber Pete is correct, it needs servicing.
The symptom you describe is often caused by a dirty venturi on this model. Do a google search for Vokera Venturi. The fan will need cleaning, and so will the heat exchanger. Various other things will need doing for reliable operation, including fitting service kit t0019.
You may be tempted to get a man round to just stop it cycling, IMHO this would be a false economy, he'l be back again before long for something that would probably have been averted by a proper service.
Phone Vokera for a local trained Corgi man, or if you use somone else make sure they know the model well, know what a flue venturi is (and the symptoms if it is dirty) and know to fit the service kit. (And check expansion vessel pressure etc etc). Should cost around 100 to 150 quid and take two or three hours. Money well spent I think.
If you dont get someone very familiar with you boiler, you could end up paying much more for a generalist to change your air pressure switch, fan etc etc in an expensive attempt to sort it the stupid way. It happens.
cd, March 2007
