So it's Vaillant for me, I have such confidence in them that I will stick my own 5 year guarantee on a Vaillant that I fit...Well I would do but if you register a Vaillant boiler, they pass the customers name on to Homeserve so that MY customer gets bombarded with letters and 'phone calls to get Homeserve to service the boiler that I fitted and I have guaranteed.....So Vaillant can go and swivel too..
I had this problem as well, so I called vaillant to find out how to stop it. Tick the box on the guarentee reg form, it will stop any info being passed on. I do this now every time and haven't had any complaints from customers being bombarded.