Baxi Bahama 100 keep cutting out?

My dreaded boiler has not had 2 sets of flow switches, cleaned at least twice, new expansion vessel etc. The problem now is that the boiler cuts out intermittantly, for both CH and DHW. The red warning light comes on, we press teh reset button and off it goes again. Can't trust the blasted thing. Heating engineer cannot think of anything to repair it.... Anybody got any suggestions as got a quote for over £2000 + VAT for a new boiler the other day.

Lena