Carbon monoxide: the alarm every gas home needs

Carbon monoxide is what you get when gas doesn't burn completely — from a faulty appliance, a blocked or leaking flue, or ventilation that's been covered over. You can't see it or smell it, which is exactly why the two defences are so important: a working alarm, and appliances serviced annually.

The symptom pattern that gives it away

Low-level CO exposure feels like ordinary illness: headaches, dizziness, tiredness, nausea. The tell is the pattern — symptoms that improve when you're out of the house and return when you're back, or several people (and pets) under the weather at once. If that describes your household, take it seriously.

The alarm

• Buy an audible CO alarm certified to EN 50291 — it'll say so on the box — not a colour-change patch.
• Fit one in every room with a gas appliance, at roughly head height and following the maker's placement instructions.
• Test the button now and again, and check the expiry date — CO sensors wear out, typically after 7–10 years, and the alarm has a replace-by date printed on it.

If the alarm sounds

• Get fresh air into the property and everyone out of it.
• Turn gas appliances off if you can do so on the way out.
• Call the National Gas Emergency line on 0800 111 999 — free, 24/7.
• If anyone has symptoms, seek medical advice and mention carbon monoxide.
• Don't use the appliances again until a Gas Safe registered engineer has found and fixed the cause.

Prevention is the annual service

Almost every CO incident traces back to an unserviced appliance or an obstructed flue. The combustion check in a proper annual service — done with an analyser, not a glance — is precisely the thing that catches a boiler starting to burn dirty. Sooting, staining around an appliance, or a pilot light burning yellow instead of blue are the visible warnings; none of them wait patiently.