Key points
- If you suspect carbon monoxide, turn off the appliance, open windows, get outside, and call the National Gas Emergency Service on 0800 111 999.
- Warning signs include yellow or orange flames instead of blue, soot or brown staining around an appliance, and a pilot light that keeps going out.
- An annual service and an audible CO alarm are the two best protections.
If you think there’s carbon monoxide in your home right now: switch off the appliance and turn off the gas at the meter if you can. Open doors and windows, get everyone outside, and call the National Gas Emergency Service free on 0800 111 999. Call 999 if anyone is struggling to breathe, confused, has chest pain or has lost consciousness.
What carbon monoxide is
Carbon monoxide (CO) is a poisonous gas produced when fuel such as gas, oil, coal or wood doesn’t burn completely. It has no colour, smell or taste. A gas appliance that’s poorly maintained, badly fitted, or has a blocked or leaking flue can produce it.
Warning signs on your appliances
The Health and Safety Executive lists these signs that an appliance may be producing CO:
- Yellow or orange flames instead of crisp blue ones. Fuel-effect fires and flueless appliances are the exception, as they’re designed to burn that colour.
- Soot or yellow-brown staining on or around the appliance.
- A pilot light that keeps blowing out.
- More condensation than usual on the inside of windows.
Symptoms of carbon monoxide poisoning
According to the NHS, symptoms include:
- headache
- dizziness
- feeling or being sick
- feeling weak, tired or confused
- chest or muscle pain
- shortness of breath
- problems with vision
They’re easy to mistake for flu or food poisoning. One clue that points to CO: the NHS notes symptoms may get worse when you spend time in an affected room or building, and better when you leave or go outside. If you think you’ve been exposed, get medical advice: call NHS 111, or 999 in an emergency.
Fitting a carbon monoxide alarm
An audible CO alarm is a cheap, essential back-up. Look for one marked as meeting BS EN 50291 and follow its instructions. As a general guide:
- Fit one in each room with a fuel-burning appliance, such as a boiler, gas fire or wood burner.
- Position it 1–3 metres away from the appliance and at least 15cm below the ceiling.
- Keep it clear of vents, extractor fans, windows and doors, and out of cupboards.
- Test it regularly and replace it when it reaches its end-of-life date.
Landlords in England have a legal duty to fit CO alarms in rooms with a fixed combustion appliance. See our landlord gas safety guide.
Prevention: servicing matters most
An alarm warns you when something has already gone wrong. Regular servicing stops it going wrong in the first place. The NHS and HSE both advise having gas appliances serviced regularly by a qualified, registered engineer, and annually is the standard. During a service we check the flue, the safety devices and how efficiently the boiler is burning, which are exactly the things that cause CO problems. See our boiler servicing page or what a service costs.
Also make sure air vents and chimneys aren’t blocked, and never use a barbecue, camping stove or generator indoors.