50E - E stands for electronic, it is not a permenant pilot! it lights on demand from the heating controls and programmer. If you can hear the fan start when the heat demand is placed, it can be either the air pressure switch at fault or the PCB (printed circuit board. look through the view window at the front, if you see a faint spark the pcb is probably ok, leaving either the gas valve or as stated - the air pressure switch. On this one as all the faults are internal, you should legally appoint a gas safe registed person to carry out the repairs.
Dave
May 2010