what is wrong with my glowworm micron50ff boiler??

my glowworm micron 50ff boiler is constantly lighting and switching itself off after a few seconds and seconds later relights, both stats(water and heating are in demand at the time )any ideas as to what the problem could be? boiler acts the same when either water or heating stat is in demand. it also stays off when in demand!! sounds a complex problem to me can anybody help please, sat listening to it fire up and shutdown as i type this.