Central heating but no hot water

[pv2512]

I have a Vaillant Combi-heater VCW sine-T3W. The central heating runs fine but does not fire up when i put the hot water tap on. If the central heating is running and i put the tap on the water comes out hot, but if the central heating is off and i put the tap on, the boiler does not fire and the water comes out cold. I recently changed the room thermostat but after chatting to a plumber friend he said it should not effect the water.
Have had diverter valve mentioned to me and a wax something or other, any help would be greatly appreciated.

 

[cross thread]

domestic diaphgram

 

[pv2512]

Is removing the diverter valve and replacing the diaphragm an easy job. Looking at it there are 4 unions to disconnect (main water in/ hot water out/ water in/out of system) along with a 3mm copper pipe. (maybe a signal?) Is it best to buy a diaphragm or actual diverter valve?
Does anyone know the manufacturers part No. for this diaphragm, after some search may be 010318.

 

[pv2512]

Have checked the diverter valve and this seems to working fine, the shaft is being driven into the switch which is working. Can hear and see it making. Only thing is the boiler doesnt fire, any more ideas?

 

[Rixy]

I also have a vaillant VCW-sine 18T3W FH combi boiler have been told it is the diverter valve or the diaphram, also been told these parts no longer available due to age of boiler can anyone tell me if this is correct. The heating works fine but can only get hot water with heating switched on

 

[pv2512]

After checking everything again. Water section, wax capsule operation and switch operation, found a hidden fuse. This had blown. Changed, now all ok.