Diverter Valve on Potterton Lynx Electronic Boiler

[lynxowner]

I have a problem with my Potterton Lynx One Electronic combi Boiler which I hope someone can help me with. The central heating is working fine but the hot water isnt working properly. When I turn on the hot tap the boiler doesnt fire up. I have looked at the diverter valve and there is a slight weep of water from around the central piston on the front. When the hot tap is opened the flow of water should push the piston out to make contact with the micro-switch assembly but the piston doesnt move far enough. I think the weeping water is evaporating and leaving the piston crusty and so preventing it moving properly. I have tried cleaning the part of the piston I can see but it hasnt helped.
The diverter valve is pretty expensive but I am wondering whether there is a diaphragm inside which I could replace more cheaply. I have the Installation and Servicing Instructions Manual but it doesnt mention anything about replacing a diaphragm. The instructions cover only how to remove and replace the whole diverter valve. The diverter valve appears to have a front section which is held in place by 8 or 10 screws around the perimeter. Does anyone know whether it is possible to get in and just replace a diaphragm? If it cant be done I think it is time to get a new boiler, it is 23 years old and probably not worth the cost of a whole new diverter valve.
Thanks to anyone who can offer advice.

 

[nickso]

yeh diaphragm can be changed on its own. easy enough job on these as long nothing else disintegrates.

 

[lynxowner]

Sounds promising. Are you sure it isnt only the later Lynx Two model on which you can do this though. Mine is a very early Lynx One. I'm wondering why the instruction manual doesnt say it can be done.
Assuming it can be done. To replace the diaphragm do I undo the screws and take the front off the diverter valve? Do I need to drain both the heating and hot water sections of the boiler to do it? Do I need any new sealing washers? Thanks again.

 

[nickso]

cant remember the difference between the two to be honest, thankfully theres very few of these beasts left round here.

if its the old giannoni valve on the right hand side it will be one nut and 6 or 8 screws to remove. you only need to turn off the mains water and open a hot tap. you will get some water spilling out but not much.

best search for a diaphragm kit, you will get all the seals you need to do the job unless it self destructs.

 

[namsag]

It wont be in instructions because when combis with these valves first came out manufacturers said whole valve had to be changed as tops had been torqued down on special machine and would leak if disturbed thus making a fortune in spares