Instead of replacing windows at great expense, let us remedy the problem by restoring them to good-as-new, saving your money. Glaze King caters for all aluminium, uPVC & timber fittings as well as doors & conservatories. Under British Standard requirement BS EN 1279, product testing for sealed units is mandatory to achieve CE compliance. FENSA is the government authorised scheme for homeowners looking to replace windows and doors. FENSA works with thousands of double glazing contractors in England and Wales.