We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.

Home & garden.

Updated: 28 Feb 2022

What to do when a carbon monoxide detector goes off

Follow our six-point plan to keep your family safe when your carbon monoxide detector's alarm goes off.
Matt Stevens

When your carbon monoxide alarm goes off, there are key steps to take to make your home safe, and to protect yourself and your family fast. 

Read on for what to do and when your detector sounds. And if you're in the market for a carbon monoxide detector, head to our best carbon monoxide detector recommendations.

Open all doors and windows

The first task is to open all of the doors and windows in the house to try to clear some of the deadly gas.

Turn off all fuel-burning appliances and leave the house

Once you’ve done what you can to ventilate your home, turn off all of your fuel-burning appliances, such as boilers and fires, and leave the house. Regardless of whether you feel ill or well, remain outside until you've spoken to a doctor or called the emergency advice line.

Don’t switch on the lights, smoke or strike a match 

Once the alarm has sounded, if there are gas appliances in your home you should avoid switching on the lights, smoking or striking a match (to light a candle for example).

Seek medical advice

If you feel ill or exhibit any of the symptoms of carbon monoxide poisoning after your alarm goes off, contact your doctor immediately or call 999 for an ambulance.

Call the emergency advice line

If you believe your carbon monoxide emergency was caused by a gas appliance, call the Gas Emergency Service on 0800 111 999. If you use oil to heat your home, call Oftec on 01473 626 298.

Arrange to have your appliances serviced

If your boiler, heater, stove or fire is producing dangerous levels of carbon monoxide, there's something wrong with it, and it will need to be serviced by a professional.

Find a recommended, local Which? Trusted Traders heating engineer in your area. And read more about what to do when a carbon monoxide detector goes off.