Saunier Duval Infineon C13e - Tankless Water Heater?

I have a Saunier Duval Infineon C13e Model 395-05 which appears to have been purchased from you. The main boiler lights intermittently and now extremely rarely. I’ve replaced the propane tank, the regulator, cleaned the water flow screens to no avail. The pilot light is battery operated and comes on just fine – there is just no lighting the main boiler. I’ve been told I need a new diaphragm and possibly another part or two. The date of fabrication as 2/2004. The serial is 0400010848. It would also be great to have instructions on how to replace such an item but first I need to find the part. Can you help?