Fire doors must be fitted by a competent individual. You should ensure that the person fitting your fire doors has had the relevant training to do so. Whatever the rating of a fire door, if it is badly fitted, it may not withstand a fire for any more than 5 minutes. There are legal requirements and specifications as set out by building regulations governing the installation of fire doors. The gap between the fire door and frame, for example, should be between 2 and 4mm. These specifications can be difficult to meet unless installation is by someone with experience and joinery skills.
The regulations around the fitting of fire doors can be confusing. Code of Practice for Fire Door Assemblies does not specify that any particular certification is required to install a fire door. However, The Fire Safety Order states that they should be installed by a competent person. That is someone with sufficient training and experience, qualifications, and knowledge.
Using a professional fire door installer will give a Responsible Person or homeowner peace of mind that the fitting has been carried out correctly and that the fire door will perform as it should in the event of a fire.