Could be this..............
Certain Potterton boliers are renowned for doing just this and the problem was highlighted about 3-4 years ago on 'Watchdog' .....If you have one that is about 6-10 years old, could be the fault they found most common on them.
It appears to be linked to the Circuit board, which keeps making it cut out ( Do you get a RED light coming on as its called LOCKOUT), and if you call Potterton and tell them the fault they may still come out and change the circuit board free of charge, as they did with anyone that had one with the same fault.
OR could be something else.....might be even thatv your Main Gas supply getting through to the house appliances is low and turns the pilot off for the bolier so it cant fire up. Tell tale sign of this is if your gas flames, if you have them, are low, even when you turn them up high.
Best of luck in finding the fault and fixing it, hairypotter :0) ( great name btw...lol )