Combi minus hot water - Suspect Diverter valve now what???

Any advice appreciated

Icon 28t combi boiler. Have to turn hot water fully on to get boiler to fire up (in summer/hot water selection)
The micro switch activated by the head of the diverter valve works ok and fires up boiler when pressed. BUT the diverter head only comes out enough when hot water tap fully on.
I am guessing the diaphragm is split/gunked up and not operating fully at lower pressure
2 questions if so
1. anyone agree or have any other ideas?
2. How big a job to inspect or replace diaphragm. Do i have to drain system or can I just undo the 8 screws on the diverter casing to get at it?
Thanks in advance

not really familiar with this model, but if its a standard giannoni diverter valve then you can just turn off the incoming main and drain the hot water off. Undo the 8 screws take the cover off and replace the diaphragm with the replacement kit.

Er, not in my exp. When you take the diaphragm out of a standard Giannoni DV a shaft comes with it. The shaft is the seal in the end of the diverting bit, so water comes out.
Let the pressure off the boiler and do up the AAV and you won't lose enough to worry about.

sometimes, but no need unless the seals in the actual dv valve body are knacked

http://www.sbplumbing.plus.com/diaphragm.jpg

I see from the pic you're right so I wonder why I remember them (ie the first one(s) I changed) peeing so much.
Perhaps the diverter shaft can get stuck in, no longer in the seal? Of course I've always assumed you have to release the pressure so haven't seen a leak recently!