Carbon monoxide and CO alarms
Checked against its sources: Updated
If a carbon monoxide alarm is going off, or you suspect CO, get everyone outside into fresh air first, stop using the appliance if you can, and don't go back in until advised.1 CO is colourless and has no smell.1
- Covers
- UK-wide for what to do; alarm rules differ by country, as shown
- You
- Get out, stop using the appliance if you can, call for help, and fit and test alarms.
- A professional
- Finding the cause and checking the appliance and flue: a Gas Safe registered engineer for gas; a competent person for oil, wood and coal.
1 What to do
Get everyone outside into fresh air first. Stop using the appliance if you can. Don't go back in until you have been advised to. From outside, call the gas emergency number: 0800 111 999 (National Gas Emergency Service, Great Britain), 0800 002 001 (Northern Ireland) or 0808 1624 444 (Isle of Man). Call NHS 111 if you think you might have symptoms. Call 999 or go to A&E if someone was exposed and is finding it hard to breathe, is suddenly confused, unconscious or weak, or has chest or muscle pain. "Do not drive to A&E."1
Official lists also say to open doors and windows and switch appliances off; do that only if it doesn't delay getting out.23 HSE warns: "CO can kill quickly without warning."2 The same goes for a boiler display: leave fault codes until everyone is safe.
2 Symptoms
NHS lists headache, dizziness, feeling or being sick, feeling weak, tiredness and confusion, chest and muscle pain, shortness of breath, a face turning hot and red (which may be harder to see on brown and black skin) and loss of vision.1 Symptoms may come and go, getting worse in the affected room or building and easing outside.1
3 Warning signs on appliances
HSE's signs of incomplete burning are yellow or orange flames instead of blue (except fuel-effect fires and flueless appliances), soot or yellow or brown staining, pilot lights that keep blowing out, and extra condensation on the inside of windows.2 CO comes from incomplete burning of fuels including gas, oil, wood and coal, so this isn't only a boiler matter.2
4 CO alarm rules
| Where | Rule | From |
|---|---|---|
| England, landlords | Alarm in any room used as living accommodation with a fixed combustion appliance, except gas cookers; repair or replace once told it is faulty6 | 1 October 2022 |
| England, any home getting a new boiler | Alarm in the room where a new or replacement fixed gas, oil or solid fuel appliance is installed, except gas used only for cooking7 | 1 October 2022 |
| Scotland, every home | Owner's responsibility: detector in the same room as a carbon-fuelled appliance such as a boiler; not needed for gas cookers and hobs8 | Date not confirmed here |
| Wales, occupation contracts | Working alarm in each room with a gas, oil or solid fuel appliance9 | 1 December 2022 |
| Northern Ireland, private tenancies | Alarm in any room or circulation space with a fixed combustion appliance or a flue10 | 1 September 2024 for new tenancies; 1 December 2024 for others |
HSE recommends an alarm as a useful precaution, not as a replacement for maintenance and safety checks.5 Alarms have a limited life, so replace them as the alarm's maker says.3
5 Prevention
NHS advises an alarm for each room with appliances burning gas, oil, coal or wood, regular servicing by a qualified, registered engineer, ventilated rooms, clean chimneys and flues, and no barbecues or camping stoves indoors.1 For servicing, see boiler service; for tenants, landlord gas safety; for a gas odour, if you smell gas. HSE says chimneys on oil, wood and coal appliances should be swept regularly.2
From the Gas Safe Register channel on YouTube. A fire service station manager explains carbon monoxide symptoms, warning signs on appliances and yearly gas safety checks, and it applies to gas appliances in any home. Nothing loads from YouTube until you press play.
Sources
- Carbon monoxide poisoning, NHS, reviewed 16 December 2025 read 3 November 2026.
- Carbon monoxide, Health and Safety Executive, page dated 10 February 2026 read 3 November 2026.
- Carbon monoxide, HSENI and gas safety and carbon monoxide, nidirect, with the number from nidirect's energy page read 3 November 2026.
- Isle of Man Government advice on gas fumes and alarms read 3 November 2026.
- CO alarm answer in HSE's domestic gas FAQ read 3 November 2026.
- Smoke and carbon monoxide alarm regulations: booklet for landlords and tenants, GOV.UK read 3 November 2026.
- Approved Document J, paragraphs 2.34, 3.43, 4.30, GOV.UK read 3 November 2026.
- Fire and smoke alarms in Scottish homes, Scottish Government read 3 November 2026.
- Fitness of homes for human habitation: guidance for landlords, Welsh Government read 3 November 2026.
- Northern Ireland statutory rule 2024 No. 123, regulation 3 read 3 November 2026.