Thanks for your posts. It seems I may have a legal argument on my hands as
to who is responsible. The clip that failed inside the boiler is right at
the bottom inside the case. My installer explained that during installation
the mains pipe connection is fitted underneath the boiler and not anywhere
near this clip fitting so I don't see how he could stress it loose. The
only thing he would pass over ther failed pipework would be the electric
plug leads for the control panel. I dont really care who is responsible as
long as someone pays. The installers explanation seemed plausible but he
did say that as Vaillaint are huge company I might not get any joy from
them. Having said that his parting shot was that from now on he would check
all the spring clip fittings upon completion of installation to make sure
they were fitted correctly at the factory. An admission of responsibility
here? I dunno. All I know is it wasn't me!

~Carl