Speaking from experience of court, get it all written down as it happens , noting dates and any costs incurred, while it's fresh in your head. You can expect a product to last at least a year and can reject the goods if they go wrong in the first six months . Record the visits on your phone as voice messages if you can
Give him a last chance to sort it out then start a court case. You will have notes, he will have no notes
The five year liability is more to do with safety, you cannot expect things to last forever