boiler back to front?

i replced the main pcb and the fan on my ikon 23t boiler(all glow worm parts) and when i put it all back together the central heating works but no hot water, and when you put it on summer mode (its a combi) it still works the heating and no hot water. when you run the hot tap the flame goes out and when you stop the hot water the flame goes back on! i have worked the micro switch and got hot water, its like its back to front!