Carbon Monoxide Safety for UK Homes — Detection Guide

The Silent Killer in Your Home

Carbon monoxide (CO) has earned its grim nickname. It is produced when any fuel — gas, oil, wood, coal, or LPG — burns incompletely. You cannot smell it, see it, or taste it. At low concentrations it causes symptoms that mimic a headache or stomach bug. At higher concentrations it kills.

Every year in the UK, CO poisoning sends hundreds of people to hospital and claims lives. The vast majority of incidents are preventable. The HSE and NHS are consistent on this point: fit an alarm, get appliances serviced, know the symptoms.

What Causes CO to Build Up

CO forms when a fuel-burning appliance cannot get enough oxygen for complete combustion. Common culprits include:

• Boilers — Especially older ones or those not serviced regularly. A cracked heat exchanger is a serious CO risk
• Gas fires and log-effect gas fires — Flues can become blocked by debris or bird nests
• Wood-burning stoves and open fires — Blocked or poorly drawing chimneys push CO back into the room
• Oil boilers and Aga-style range cookers — The same risks apply as with gas
• Portable generators — Should never be run indoors or in a garage attached to the house
• Gas cookers — Generally lower risk, but prolonged use in a poorly ventilated kitchen can raise CO levels

Symptoms to Recognise

CO poisoning mimics other illnesses, which is why it often goes undiagnosed. Suspect CO if:

• More than one person in the household feels unwell at the same time
• Symptoms improve when you leave the house and return when you come back
• Pets seem lethargic or unwell
• Symptoms include some combination of: headache, dizziness, nausea, shortness of breath, confusion, or chest pain

Severe CO poisoning causes loss of consciousness and can be fatal within minutes. Do not wait to see whether things improve.

What to Do When Your CO Alarm Sounds

A CO alarm sounding is an emergency. Treat it exactly as you would a fire alarm:

1. Get everyone out of the property immediately
2. Leave the door open to ventilate as you go
3. Call 999 from outside — the fire service responds to CO alerts
4. Call the National Gas Emergency Service on 0800 111 999 if the source is likely a gas appliance
5. Do not go back inside for any reason until told it is safe
6. Seek medical attention even if you feel fine — CO can continue to cause harm after exposure

Where to Fit CO Alarms

The positioning of CO alarms matters. Follow this guidance based on HSE and alarm manufacturer recommendations:

Avoid fitting alarms directly above cookers or in very humid spots such as bathrooms, as this can cause false alerts. Do not fit them in corners where air circulation is poor.

Annual Servicing — The Most Important Prevention Step

Most CO incidents result from appliances that have not been maintained. The law requires landlords to arrange annual gas safety checks, and the same logic applies whether you own or rent:

• Gas boiler — Annual service by a Gas Safe registered engineer
• Oil boiler — Annual service by an OFTEC registered engineer
• Wood-burning stove and open fireplace — Chimney swept at least once a year (twice if burning coal or using heavily)
• Gas fire — Annual check, including flue inspection

Never block ventilation around appliances. The slots and airbricks around a gas fire or boiler are there for a reason — blocking them with furniture or draught excluders can cause CO to accumulate.

What the Law Says

For Owner-Occupiers

The law does not currently require owner-occupiers in England to fit CO alarms everywhere, but the HSE and NHS strongly recommend them. In Scotland, CO alarms are a legal requirement in any room with a fuel-burning appliance.

For Landlords in England

Under the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, private and social landlords in England must:

• Fit a CO alarm in any room with a fuel-burning appliance (excluding gas cookers)
• Ensure alarms are in working order at the start of each tenancy
• Repair or replace alarms when told they are faulty by tenants

Failure to comply can result in a civil penalty of up to £5,000.

For Tenants

If you rent and there is no CO alarm fitted near your boiler or other fuel-burning appliance, report this to your landlord in writing. If they fail to act, contact your local council's environmental health department. You can also contact the HSE on 0300 003 1647.

Choosing a CO Alarm

Look for alarms that carry the BSI Kitemark and meet BS EN 50291. This is the standard used across the UK and means the alarm has been independently tested.

Alarms typically last 5–10 years depending on the model. Check the end-of-life date printed on the back and replace when due, even if the alarm appears to work.

What You Need

Key Contact Numbers

Carbon monoxide poisoning is one of the most preventable causes of accidental death in UK homes. A detector costs under £20 and lasts a decade. Annual appliance servicing is rarely more than £100. Both are far less than the cost of doing nothing.