baxi solo 3 shuts down after approx 1min if it turns on at all -HELP?

just moved into a house with a baxi solo 3 boiler, it looks quite new but most of the time does not switch on! if it does kick in it only lasts a minute and then shuts down, we have tested all the electrics for voltage and continuity, replaced potentiometer and stripped all the other parts down and checked them but nothing, i dont want to fork out loads if i dont need to. any suggestions would be greatly appreciated as we have completely run out of ideas and its COLD thanks