Carbon monoxide

Carbon monoxide

Carbon monoxide (CO) is the most common form of household poison. You can't see it, taste it or smell it. Carbon monoxide poisoning can be fatal or cause permanent damage to your health.

Get advice on what to do if you think you have carbon monoxide poisoning, where to put your carbon monoxide alarm, what kind of carbon monoxide alarm to buy and how to avoid carbon monoxide poisoning.

What to do if a carbon monoxide alarm goes off

If your carbon monoxide alarm is beeping, immediately get out of the building and call the relevant helpline for the fuel type: gas emergency helpline 0800 111 999.

Call a registered engineer to check all your fuel-burning appliances. To check if an engineer is on the gas safe register visit

In a medical emergency, don't delay, and call 999 immediately. 

What is carbon monoxide poisoning?

The early symptoms of poisoning can be easily confused with many common ailments and can develop quickly or over a number of days or months. Look out for:

  • a headache - this is the most common symptom
  • feeling sick, dizzy, tired and confused
  • being sick and having stomach pain
  • shortness of breath and difficulty breathing.

Read more about carbon monoxide poisoning on the NHS website.

What to do if you think you have carbon monoxide poisoning

If you think you have carbon monoxide poisoning, you should:

  1. leave the building immediately and get out into the fresh air
  2. switch off all your fuel-burning appliances and open windows on your way out
  3. seek urgent medical advice from either your GP (for low levels of carbon monoxide) or your Accident and Emergency department if you think you have been exposed to high levels

If you think there is an immediate danger, call the Gas Emergency Helpline on 0800 111 999 or the relevant service for your area. Call a registered engineer to check all your fuel-burning appliances. To check if an engineer is on the gas safe register visit

Carbon monoxide alarms

  • You need a carbon monoxide alarm or detector near any fuel-burning appliance you have.
  • You should have one in every room where there is a fuel-burning appliance.
  • Carbon monoxide alarms work by detecting carbon monoxide in the room.
  • They rarely beep as a false alarm so if your carbon monoxide detector is beeping you should act fast and get out of the property.
  • Carbon monoxide detectors should only be used as a back-up precaution. They aren’t a substitute for proper installation and maintenance of fuel-burning appliances.
  • If you are in a rented property, landlords are required by law to install working smoke and carbon monoxide alarms in their properties.
  • Test your alarm regularly, at least once a month.

Do I need a carbon monoxide alarm as well as a smoke alarm?


Unless you have a specific combined smoke and carbon monoxide alarm, you will need a separate smoke alarm. Carbon monoxide alarms do not detect fire, so you should make sure you also have a working smoke alarm on every level of your home.

What carbon monoxide alarm should I buy?


Carbon monoxide alarms are available from DIY and hardware stores. Make sure the alarm meets British Standard EN50291 and ideally the British Standard Kitemark. You should install, check and service carbon monoxide alarms according to the manufacturer's instructions.

Where should I place a carbon monoxide alarm?


You should place a carbon monoxide alarm near every fuel-burning appliance you have. Read the instructions for your specific alarm, but this is usually suggested to be 1-3 metres away from the appliance. This could mean that you have several alarms. For example, one in your kitchen near the gas stove and boiler, but also one in the lounge near a fire.

Preventing carbon monoxide poisoning

The first thing to do to reduce the risk of carbon monoxide poisoning is to install a carbon monoxide alarm or detector. 

Use a reputable, registered engineer to install and service your boiler, cooker, heating system, and appliances. Never attempt to install or service appliances yourself.

Anyone carrying out work on installations and appliances in your home must be registered with a relevant association, such as the:

Make sure all chimneys and flues are clear, and vents aren’t covered. Have your chimney regularly swept by a qualified chimney sweep who's a member of the: 

Carbon monoxide causes

Carbon monoxide occurs when a fuel-burning appliance has not been properly installed, maintained, or is poorly ventilated. Carbon monoxide can come from: 

  • boilers
  • gas fires
  • central heating systems
  • water heaters
  • cookers
  • open fires and wood-burning stoves.

If the fuel in any of these appliances does not burn fully, carbon monoxide (CO) gas is produced.

Spot the signs of carbon monoxide

  • Yellow or orange flames, rather than blue flames (except fuel effect fires or flueless appliances which display this colour flame).
  • Soot or yellow/brown staining around appliances or fireplaces.
  • Pilot lights that frequently blow out.
  • More condensation inside windows than you would usually have.

Reduce the risk of carbon monoxide poisoning outside the home

  • Only use a barbecue outdoors and in well-ventilated areas (and never in a tent or caravan).
  • Do not leave cars, petrol-fuelled lawnmowers running in the garage.
  • Take care with paint cleaning and removal products. Fumes from cleaning fluids and paint removers that contain methylene chloride (dichloromethane) can also cause CO poisoning. Try to choose products that are water-based and don’t contain harmful solvents.

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