How can I fix my Chaffotaux & Maury HE combi boiler?

When you turn the hot tap on the boiler fires up but then after a few seconds it stops working and EO4(no flame detected) comes on the screen, usually if I leave the hot tap on it will eventually right itself, but lately it's taking longer to do that as EO4 keeps coming up, plus sometimes E18(flame lift) comes up, then other times AO3(no flame after safety timer) comes up which means I have to press the reset button. It's very frustrating and even my plumber does not seem to be able to fix it. The boiler is 4 years old and has already had the mother board replaced plus the central heating clock does not work and you cannot replace it, so for that I have to manually turn it on when I need it, which is a pain when you're not in.