Gas boilers are designed to perform at a high level for many years, withstanding wear and tear from constant heating up and cooling down, and the parts that carry gas must be certified to ensure they are safe.
Parts that are not supplied by the manufacturer, or have been refurbished, are not approved for use in boilers and do not carry the right certification. They can be unreliable, made from poor quality materials, and could be dangerous. They could lead to poor reliability of the boiler, costly call-outs and could make the boiler warranty invalid.
The person responsible for selling or installing counterfeit boilers parts, whether they are refurbished, reconditioned or modified, risks their reputation and is liable in the event of a prosecution.
A business selling copy parts becomes the manufacturer and, along with the installer, is liable for the safety of the part once it is installed. If they advertise the part, the seller is also breaking copyright and trademark laws and can be prosecuted.