Carbon monoxide (CO) is an odourless, colourless gas produced by incomplete combustion. A faulty or poorly maintained gas boiler is one of the most common sources in domestic properties.
Why CO is so dangerous
CO binds to haemoglobin in the blood 200 times more strongly than oxygen, preventing oxygen delivery to organs. At low concentrations, symptoms are flu-like (headache, nausea, dizziness). At higher concentrations, CO causes unconsciousness and death — often during sleep.
Legal requirement for CO alarms
Since October 2022, a carbon monoxide alarm is legally required in any room where a fixed combustion appliance is installed (boilers, gas fires, log burners). This is a legal requirement for both homeowners and landlords.
Choosing a CO alarm
Buy an alarm with the British Standard Kitemark (BS EN 50291). Standalone battery alarms: replace batteries annually, replace the alarm every 5–7 years. Mains-wired alarms: typically more reliable. Combination smoke/CO alarms are acceptable.
Where to position it
In the same room as the boiler, at head height (CO is slightly lighter than air but mixes quickly). Not directly next to the boiler or in the flue path.
What to do if it alarms
- Leave the property immediately — don't waste time
- Leave the door open
- Call the National Gas Emergency number: 0800 111 999
- Don't re-enter until cleared by an engineer