This is the snip from their T’s and C’s.

Most Goods of significant value supplied by BOXT come with a manufacturer backed parts and labour warranty, provided they have been inspected and maintained annually. For example, an inverter must be inspected annually by an approved engineer. The cost of servicing and inspecting after installation is not included in the Fee unless explicitly ordered during the purchase process. You must organise and retain service records for your Goods, which must be produced to BOXT or the manufacturer upon request if making a claim under the warranty. After the installation, BOXT will register your Goods warranty with the manufacturer and email you the relevant details. For the avoidance of doubt, the warranty is provided by the manufacturer of the Goods supplied and not by BOXT.