Thats the same model as the Biasi,the divertor valve is Black plastic 3 way actuator and situated on the left hand side of the boiler,sometimes that plays up or the brass body needs to be refurbished You are gonna have fun considering you dont even know what it looks like,still charging people simon?
you can get a kit to overhaul the valve, about £40 i think, although if this is siezed it'll have knackered the motor on top. Glow worm swiftflow, they dont have a diverter either.
yes dead right mate work like the old gas geysers (twin pass heat exchangers) there's a few combi's like that.