How poor combustion and faulty flueing create a carbon monoxide risk, how to prevent exposure, and what to do first if it is suspected.
Carbon monoxide comes from incomplete combustion, and you cannot see or smell it. Too little combustion air, poor maintenance or wrong adjustment can make more of it. A blocked or faulty flue can let combustion products into occupied rooms.
How an everyday fault becomes a CO risk
- A covered or blocked combustion-air vent starves an open-flued appliance of air. Too little air gives incomplete combustion, and incomplete combustion produces carbon monoxide.
- A blocked flue stops the products of combustion getting away, so they can enter the room.
- Ventilation and flue performance have to be assessed together.
- A normal-looking flame or a silent CO alarm does not mean the appliance is safe.
Prevention
- Keep required vents and flues clear.
- Have appliances maintained regularly by a Gas Safe registered engineer.
- Treat a CO alarm as a back-up warning, never a substitute for servicing.
- Where an appliance needs an air vent, the vent must be permanently open and non-adjustable. An openable window or an adjustable trickle vent can be shut at any time, so neither can take the place of a vent that has been covered or blocked: restore the vent itself.
If exposure is suspected
Headache, dizziness or nausea affecting several people indoors, or easing outside, are reasons to suspect carbon monoxide. Take a sounding alarm seriously even when nobody feels unwell.
- Get everyone into fresh air and stop using the suspect appliance; switch it off only if that is safe.
- Get medical help. After suspected exposure, call 999 if someone struggles to breathe, becomes suddenly confused, loses consciousness, feels weak, or has pain in their chest or muscles. For other possible CO symptoms, contact NHS 111 urgently. An affected person must not drive.
- Report the suspected gas-appliance incident on 0800 111 999 from a safe place, and stay out until you are told it is safe to return.