Commonly known as the "silent killer," carbon monoxide leaks can be incredibly difficult to detect, as the gas is both odourless and silent.
Since exposure can have fatal consequences, it’s important to be well-informed about the signs, causes, symptoms and preventive measures you can take, which our experts have explained below.
From installing a carbon monoxide detector to getting annual checks from a Gas Safe engineer to prevent things like boiler problems, there are many steps you can take to keep your home and family safe throughout the year.
What are the signs of a carbon monoxide leak?
Carbon monoxide leaks can be hard to spot, but Adam Knight, Lead Engineer at BOXT, says to look out for the following signs:
- A soft yellow flame instead of a clear blue one
- Sooty marks around the boiler or vents
- Leaks and heavy condensation (specifically on the inside of window panes)
- Pilot lights that keep going out
- Unusual smells (which can be anything out of the ordinary coming from the appliance)
- New or unusual boiler noises, such as banging, whistling, humming or clicking
- Symptoms consistent with carbon monoxide exposure
Adam Knight is a Lead Engineer at heating and cooling experts, BOXT. Adam brings over 17 years of industry experience, including 14 years at British Gas specialising in auditing, gas qualifications, and incident investigations, and now leads BOXT’s Tech Survey Team with specialist training in air conditioning and heat pump systems.
What should you do if there’s been a carbon monoxide leak?
If you suspect a carbon monoxide leak or have noticed any of the signs above, Adam Knight recommends taking these steps:
- Switch off the appliance
- Turn off the gas if it's safe to do so
- Open your windows to ventilate the area
- Leave the property immediately
- Contact a Gas Safe engineer or call the National Gas Emergency number on 0800 111 999 before anyone goes back inside.
How to prevent a carbon monoxide leak
To prevent a carbon monoxide leak, make sure your home is fitted with working safety alarms (smoke and carbon monoxide), and remember to test them regularly.
Adam Knight also advises avoiding blocked flues, chimneys, or vents, and staying alert to warning signs such as changes in flame colour, sooty marks, leaks, unusual smells or noises, heavy condensation, or unexplained increases in energy bills.
He adds, "Prevention starts with annual checks from a Gas Safe registered engineer (like the annual servicing BOXT can arrange)."
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What causes a carbon monoxide leak?
Carbon monoxide leaks can be caused by a number of factors, including blocked flues, chimneys, or vents, as well as ignoring the warning signs above, which can ultimately lead to an incident.
Adam Knight adds, "Carbon monoxide leaks can be caused by faulty or poorly maintained boilers or gas appliances, particularly if they have not had annual checks by a Gas Safe registered engineer."
Symptoms of carbon monoxide poisoning
If you have been exposed to carbon monoxide, you may experience the following symptoms:
- Headache
- Dizziness
- Shortness of breath
- Confusion
- Weakness
- Chest and muscle pain
- Nausea
Dhara Patel, Physician at Kuon Healthcare, warns, "CO exposure symptoms can be delayed, and it may be a long time until symptoms are first felt. While symptoms may improve after some time in fresh air, medical advice should be sought.
"Children, pregnant people, elderly people, and people with heart or lung diseases are the most at risk. If any such symptoms are present, or confusion, vomiting, or loss of consciousness are present, it is critical to seek medical help."
CO gas prevents the brain and heart from getting the oxygen they need, making it extremely hazardous to your health, explains Dhara. In extreme cases, exposure may even lead to unconsciousness or death.
Dhara Patel is a GMC-registered GP Physician Associate (PA-R), with more than four years of experience across the NHS and the private sector.
According to the National Institute for Health and Care Excellence, approximately 40 people in England and Wales die each year from carbon monoxide poisoning. Incidents are more common during the winter, when heating appliances are used regularly.
Feeling unsure whether your heating system needs an upgrade? Read our expert guide on when to replace a boiler and learn about the different types of boilers you might want to consider.
