sime superformat 100e boiler starts up andthe pilot goes out?

when the boiler kicks in pilot comes on but when the
boiler comes in on its cycle the pilot does not ignite
have to then flick control switch from on to off and
back to on for the pilot light to come on
i have had 4 corgi reg engineers out to have a look
at the problem but with no joy ,this problem with the boiler goes on about 10 times a day
sime super format 100e boiler installed 2002