worcester 9.24 no hot water?

please help, i'm pulling my hair out. it first began with the boiler only giving hot water when the central heating was on. i have checked the diverter valve, and the pin rises perfectly and pushes the micro switches. so i have replaced the micro switches.at first there was no change, just the same as before. now i only have central heating, and if i turn a hot tap on the second the micro switches click the demand light goes out and the boiler shuts down? can anybody help????