Hi, I have bought few radiators from an online retailer six years ago. The paint is peeling off and they are rusting away - very ugly to see. I contacted the seller with pictures and invoices/codes of my orders. The supplier replied that "they want see a full invoice from who installed your radiators with all the work carried out in the invoice. This must be provided by a professional plumber". I haven't yet found the plumbers' invoice (6 years ago!) - wondering who keeps paper invoices for plumbing jobs these days! The Radiators are covered by 20 years warranty. What if I cannot find the invoice - can I challenge the supplier to get a warranty cover? Many thanks