worcester combi boiler cutting out?

i have a worcester bosch 240 combi boiler, central heating works fine but when we use hot taps[especially the mixershower] the pilot goes out after about 2 minutes.we have had 2 plumbers look at it,both could`nt find a problem with the boiler and suspected water pressure problems. water board came out and said pressure was above normal.this is now becoming annoying as showers have to be abit quick unless someones on standby to press the re set button ! can anyone help ?