Recognise carbon monoxide symptoms, act on them first, explain what an alarm can and cannot do, and know when Approved Document J calls for one.
Why symptoms matter
Carbon monoxide can form when combustion is incomplete. It has no colour, smell or taste, so a person may first notice a headache, nausea, dizziness, tiredness, weakness, breathlessness, confusion or chest pain. These complaints can be misread as flu or overwork. Ask who feels ill and where. If several people are affected together, or someone feels better outdoors and worse again inside, suspect CO exposure and act at once.
Public CO guidance gives you a consistent message on symptoms and urgent action to pass on to customers on every visit. It supports your professional duties; it does not change them.
Act first
- Treat a sounding alarm or suspected exposure as real and get everyone into fresh air.
- Get medical help promptly: call 999 for breathing difficulty, sudden confusion, unconsciousness, weakness, or chest or muscle pain after suspected exposure. For other possible symptoms, contact NHS 111 urgently. An affected person must not drive.
- Turn off the suspect appliance if it is safe to, and report the gas hazard from a safe place. Do not delay urgent medical help.
- Do not go back in or use the appliance again until you have the right advice and a competent person has checked it.
When a customer reports repeated headaches with a lazy yellow flame or staining, protect people before discussing servicing. Do not delay getting out to investigate, to open every window or to reach a control that is unsafe to get to.
What an alarm is, and is not
Prevent exposure by keeping the appliance, combustion-air path and flue sound and by servicing it. A CO alarm warns when the CO at its sensor reaches its alarm level; it cannot stop the appliance making CO. A silent alarm never outweighs symptoms or a measured analyser reading. Site and test the alarm to its instructions, then replace it at the end of its marked working life.
When Approved Document J calls for an alarm
In Approved Document J, J3 is the carbon-monoxide warning requirement. The other requirements cover combustion air (J1), removing combustion products (J2), and protection from heat and fire (J4).
- When: in England, where a new or replacement fixed gas appliance is installed in a dwelling, an alarm should be provided in the room where the appliance is. Replacing a combi boiler brings this in. Appliances used solely for cooking are excluded, and extending pipework installs no appliance.
- Which alarm: one that meets BS EN 50291-1 and runs on a battery designed to last its working life, with a warning when that life is due to end. A fixed-wired mains Type A alarm with a sensor-failure warning is the alternative. Plug-in alarms are excluded, and replaceable batteries depend on somebody remembering to change them.
- Where: on the ceiling at least 300 mm from any wall, or high on a wall above any doors and windows but not within 150 mm of the ceiling, and between 1 m and 3 m horizontally from the appliance. Follow the alarm manufacturer's instructions as well.