Doors, windows & security
Carbon monoxide alarms: the five-minute brief
Carbon monoxide is made whenever a fuel burns without enough air, and you cannot see, smell or taste it. An alarm is the only reliable warning you get. Five minutes covers what matters: where alarms go, what to do when one sounds, and who must fit them by law.
By the Tickover team · Published 18 February 2026 · 4 min read
How urgent is this?
A sounding CO alarm means act now
Fresh air first, investigation later. Work through the steps below and do not go back inside until you are told it is safe.
Where carbon monoxide comes from
Any appliance that burns fuel can produce carbon monoxide when combustion goes wrong or a flue stops doing its job: gas boilers, hobs and fires, log burners, open fires, oil boilers, portable generators and barbecues. The usual causes are missed servicing, blocked flues and chimneys, and appliances run in spaces they were never designed for. A barbecue brought into a tent or garage is the textbook example.
Prevention is two habits: an annual boiler service by a Gas Safe registered engineer, and a swept chimney if you burn wood or coal. The alarm is the backstop, not the plan.
If the alarm sounds
Do this, in this order
Open doors and windows
Get fresh air moving through the rooms straight away.
Turn off fuel-burning appliances
Boiler, fire, hob, log burner: off, if you can do it quickly on the way.
Get everyone outside
Into open air, pets included, and stay out.
Call 0800 111 999
The National Gas Emergency line, free and staffed around the clock.
Seek medical advice
Tell them carbon monoxide is suspected, even if everyone feels fine by then.
Afterwards, the appliances stay off until they have been checked: a Gas Safe registered engineer for anything gas, a qualified sweep or HETAS technician for solid fuel. An alarm that sounded was doing its job; the appliance that made it sound has not finished being a problem.
Where alarms go
Placement rules
- One alarm in every room with a fuel-burning appliance
- Add one to any bedroom a flue passes through
- 1–3 metres from the appliance, measured horizontally
- At head height: a shelf or wall bracket is fine
- Not directly above a cooker, fire or boiler
- Away from windows, doors, extractor fans and vents
- Not inside a cupboard or hidden behind curtains
- Look for BS EN 50291 on the box before buying
As a guide, a sealed ten-year alarm from a mainstream brand costs £15 to £30, needs no battery changes, and gets replaced whole at the date printed on the case. Press the test button monthly, the same rhythm as your smoke alarms, and take it with you when you camp or use a holiday cottage with a stove.
What landlords must provide
In England, landlords must fit a carbon monoxide alarm in every room used as living accommodation that contains a fixed fuel-burning appliance, with gas cookers the one exception, and must repair or replace an alarm promptly once told it is faulty. Scotland and Wales have their own versions of the rule with the same intent. If you rent and the alarms are missing, ask in writing and keep a copy.
Owned or rented, CO alarms earn a slot in the annual security walk-round alongside the locks and lights: one test button each once a month, and a date check once a year.
Not sure what you’re dealing with?
Unsure whether an alarm, an appliance or a symptom needs action tonight? Tickover Self-Diagnose walks you through it and lines up a vetted Gas Safe registered engineer if one is needed.
Quick answers
Where should a carbon monoxide alarm be placed?
In every room with a fuel-burning appliance, one to three metres from the appliance measured horizontally, at roughly head height on a wall or shelf. Keep it out of cupboards, away from windows, vents and extractor fans, and never directly above a cooker, fire or boiler. Add alarms in bedrooms a flue passes through, and check for BS EN 50291 on the packaging.
What are the symptoms of carbon monoxide poisoning?
Headache is the most common, followed by dizziness, nausea, tiredness, breathlessness and confusion. The pattern matters more than any single symptom: feeling better in fresh air and worse back indoors, or the whole household unwell at once, points to carbon monoxide. If that pattern appears, get outside, call 0800 111 999 and seek medical advice the same day.
Do landlords have to provide carbon monoxide alarms?
Yes. In England a landlord must fit a CO alarm in every room used as living accommodation with a fixed fuel-burning appliance, apart from gas cookers, and must repair or replace a faulty alarm promptly once informed. Scotland and Wales apply similar rules. Report a missing or dead alarm to your landlord in writing and keep a copy of the message.
How long do carbon monoxide alarms last?
Most modern units are sealed, with a battery designed to outlast the sensor, typically seven to ten years, and carry a replace-by date on the case. The sensor degrades whether or not the alarm ever sounds, so the date applies regardless. Test monthly, and replace the whole unit at the printed date, or sooner if it fails a test.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
Keep reading
Doors, windows & security
Smoke alarm beeping? Decode it and make it stop
One chirp a minute, three beeps, or a full siren at 2am: what each smoke alarm sound means, which battery fixes it, and when the unit has expired.
4 min read
Heating & hot water
What actually happens in a boiler service
What a boiler service actually includes, how long it takes, what it costs, why it protects your warranty, and why summer is the clever time to book.
4 min read
Roof, walls & outside
Chimneys and log burners: sweep, check, burn
How often to sweep for wood and smokeless fuel, what Ready to Burn means, the cowl and flaunching checks from the ground, and why the CO alarm is not optional.
4 min read