Baxi Combi Instant 105e - flow problem

My Baxi combi has a flow problem. Over a period of time I've had to open more and more h/w taps to get the boiler to light and supply h/w. Now it's got to the stage where no matter how many taps I open the boiler won't light automatically. The only way I can get it to light is by opening a tap and with the tap still running, cycle the boiler off/on at which point the h/w neon glows, the boiler lights ,the flame neon glows and 'hey presto' h/w. At no point do I have any flashing fault neons. Any ideas?
Thanks
Adrian

diaphram in diverter valve would be first call.