why does the pilot light not relight after the water pressure has dropped?

There is a small leak in my boiler (yes, I know this needs to be fixed but in the meantime...) which means the water pressure drops. Whenever this happens without me noticing quickly enough ie without me topping up the water, i then have great trouble relighting the pilot light. Any ideas? i've tried oiling the fan and i've checked the air pressure switch, both seem ok. In the past it has relit itself after i've pressed the reset button a few times but alas, this method isn't working now. please, can anyone help? thanks in advance for any time you spend helping me
the boiler is a Ravenheat RSF 100ET

Nicola
August 2007