If you smell gas, suspect carbon monoxide or feel unwell around a gas appliance, leave the property, avoid flames and electrical switches, and use the official emergency guidance immediately. In Great Britain, the National Gas Emergency Service number is 0800 111 999.\n\nNever remove a boiler casing or attempt a gas repair yourself. Gas work must be carried out by a suitably qualified Gas Safe registered engineer.\n\nFit an audible carbon monoxide alarm that meets the relevant British Standard, follow its placement instructions and test it regularly. An alarm supports professional maintenance; it does not replace it.\n\nArrange regular servicing in line with the manufacturer’s instructions. Ask to see the engineer’s Gas Safe ID card and check that the categories on the back cover the work being completed.\n\nThis guide is a starting point, not emergency diagnosis. Follow the linked Gas Safe Register guidance whenever there may be an immediate risk.