Diverter valve problem?

I've an ICON T combi boiler - no further ID, sorry. Gets CH but no DHW. Help from another forum suggests Diverter valve problem. Think I've found this - brass assy with a plunger out of the top. This plunger does not make associated microswitch with hot tap on. With tap on, if I manually make m/s, boiler fires up. Is this the diverter valve? If so, any repairs or should I replace? Any info appreciated. Thanks. Mike.