The response sequence for a suspected gas escape or carbon monoxide, and where a non-Gas-Safe-registered plumber's role ends.
Treat a gas smell, a sounding carbon monoxide alarm, or symptoms that fit carbon monoxide poisoning as an emergency, even in the middle of unrelated plumbing work.
Get people out before anything else
Get everyone into fresh air straight away rather than staying to investigate, operate a switch or appliance, or finish the job first. Avoid naked flames and electrical switches near a suspected escape, since either can ignite it. Once everyone is clear, call the gas emergency service on 0800 111 999 from a safe place. Open an accessible door or window, or close a safely reachable emergency control valve, only if this does not delay leaving or mean entering the affected area.
Carbon monoxide gives no warning of its own
Carbon monoxide has no smell, colour or taste, so a clear "no gas smell" proves nothing about it. Recognise it instead by its warning signs: headaches, dizziness or nausea that several people in the house share and that ease when they are away from the property, sooty or yellow-brown staining around an appliance or flue, and a lazy, yellow or orange flame where the burner should show a crisp blue one. Any of these gets the same response as a suspected escape — fresh air, medical advice if anyone has symptoms (999 for severe symptoms such as breathing difficulty, confusion or collapse), and the appliance left unused. Do not wait for a carbon monoxide alarm to sound before acting on these signs, and treat a sounding alarm as real rather than a false alarm.
Stay within your registration
A plumber who is not Gas Safe registered must not investigate, test, adjust or repair a gas appliance or its combustion, however straightforward it looks, and a customer's consent or a promise to have the work signed off afterwards does not change that. Make the situation safe, report it, and refer the gas work to a Gas Safe registered engineer. A water-side fault found on the same visit can still be dealt with if it is within your own competence and does not delay protecting people from the gas or carbon monoxide risk.
An appliance made safe still leaves a customer without heat
Turning off a dangerous gas appliance is not the end of your responsibility, especially for a vulnerable customer in cold weather. Advise safe temporary warmth, such as plug-in electric heaters and warm clothing, never a gas oven or hob, and make arranging a Gas Safe registered engineer a priority rather than leaving it for a routine appointment.