What is Gas Installer Assessment (ACS/GIAR)?

Before joining the Gas Safe Register, a gas engineer must hold a current ACS (Accredited Certification Scheme) qualification, which includes a core gas safety assessment (CCN1 for domestic) plus appliance-specific modules such as boilers (CENWAT) or cookers (CKR1). Certificates are renewed every five years through reassessment. The assessment proves practical competence and underpins legal registration; it is sometimes referred to alongside the Gas Industry Accident Reporting (RIDDOR) duties engineers must follow.