Vokeras of a certain age had issues with the flue venturi, slightest build up of dirt causes the classic hot/cold/hot cycling. If you can handle a multimeter, have the service manual and know there are mains voltages involved, you can monitor the state of the flue venturi pressure switch when the boiler cuts out. You need to take the venturi out to clean it properly, as its in the combustion chamber one is obliged to say this is a job for a corgi man, in case you gas your family with carbon monoxide.... It could just be the differential switch in the flue is signalling a real blockage.... but my guess is it just needs cleaning.
c, February 2011
