fault with biasi boiler?

we have a biasi 32s boiler, which the flame goes off leaving no heating no hot water, you then have to turn the heating down to the lowest point wait a few seconds then turn it back on to get the heating back on and the hot water, in the summer when the heating is off, this does not happen only when the heating is on. some days it goes off four to five times other days it doesnt go off at all, heating engineers are baffled can you help at all