Carbon Monoxide and Boilers: Signs, Risks, and How to Stay Safe

What is carbon monoxide?

Carbon monoxide (CO) is a poisonous gas produced when fuel burns incompletely. A properly working boiler produces very little CO, and what it does produce is safely vented through the flue. A faulty boiler, blocked flue, or poor ventilation can cause CO to leak into your home. You cannot see, smell, or taste it.

Signs of a carbon monoxide leak

On the boiler:

• A yellow or orange flame instead of a crisp blue one
• Black soot marks or staining around the boiler
• The pilot light keeps blowing out
• Increased condensation on windows near the boiler

On you and your family:

• Headaches, dizziness, or nausea
• Breathlessness or confusion
• Symptoms that improve when you leave the house

If multiple people in the household have these symptoms at the same time, take it seriously.

What to do if you suspect a leak

1. Stop using the boiler - turn it off immediately
2. Open windows and doors to ventilate the property
3. Leave the house and take everyone with you
4. Call the National Gas Emergency number from outside: 0800 111 999
5. Go to A&E if anyone has symptoms - tell them you suspect carbon monoxide

Do not go back inside until an engineer has checked the property.

How to prevent carbon monoxide poisoning

• Get your boiler serviced annually by a Gas Safe registered engineer
• Fit a carbon monoxide alarm in every room with a gas appliance (they cost £15-£25 and could save your life)
• Never block air vents or flues
• If your boiler is old and showing signs of wear, get it checked or replaced

Carbon monoxide alarms

Every home with a gas boiler should have at least one CO alarm. Fit it in the same room as the boiler, at head height or on the ceiling. Replace it every 5-7 years (check the manufacturer’s guidance). They are cheap and they work - do not rely on being able to spot the signs.