So it is rumour. If a maker rejects a guarantee they had better put it in writing stating where the installation is flawed. If it is not, a sharp email pointing out where they are wrong, and that if they do not honour the guarantee legal action will be pursued, and that you will go for costs if you are forced into the legal route. They will take the easy way out and fix it in 99% of cases.My apparently is me not having first hand experience of this but having it on good information. Ask around it's common knowledge