Historic UK government guidance estimates that carbon monoxide poisoning causes around 200 hospital admissions each year, although annual death figures vary according to the period and incidents included.
The main problem with carbon monoxide is that you cannot see, smell, or taste the gas.
That’s why a carbon monoxide alarm is one of the few ways to spot a dangerous build-up before anyone gets sick.
Carbon monoxide can build up if you have a faulty boiler, a poorly maintained fire, a blocked or damaged flue, or if you use fuel-burning equipment in a closed space.
Spotting the symptoms early and acting quickly can save lives.
What Should You Do If You Suspect Carbon Monoxide?
If your carbon monoxide alarm goes off, or you think someone might have been exposed:
- stop using the suspected appliance if it is safe to do so
- open doors and windows to ventilate the room
- leave the property and move into fresh air
- do not return to the affected building until you have received advice
- call the National Gas Emergency Service on 0800 111 999 if a gas appliance may be involved
- seek prompt medical advice and explain that carbon monoxide exposure may have occurred.
Call 999 or go to A&E if someone is struggling to breathe, suddenly becomes confused, loses consciousness, feels severely weak or develops chest or muscle pain.
Don’t assume your home is safe just because the alarm has stopped. Don’t use the suspected appliance again until a qualified professional has checked and confirmed it is safe.
What Is Carbon Monoxide?
Carbon monoxide, or CO, is a harmful gas made when fuels like gas, oil, coal, or wood don’t burn the right way.
This can happen when an appliance is faulty or does not receive enough oxygen.
Possible household sources include:
- gas boilers
- gas fires
- oil boilers
- wood-burning stoves
- open fires
- coal fires
- gas water heaters
- portable gas heaters
- barbecues
- camping stoves
- petrol-powered generators
Carbon monoxide can also enter a property through a damaged, blocked or incorrectly installed flue.
Although gas appliances are commonly associated with carbon monoxide, any combustion appliance can potentially produce it. This includes appliances that burn oil, wood and coal.
Why Is Carbon Monoxide Dangerous?
When carbon monoxide is breathed in, it enters the bloodstream and prevents the body from carrying oxygen properly.
This means vital organs, including the brain and heart, may not receive the oxygen they need.
The brain and heart are especially vulnerable to reduced oxygen levels.
The effects depend on several factors, including:
- how much carbon monoxide is present
- how long the person is exposed
- the person’s age
- their general health
- whether they are asleep
- whether they have an existing heart or respiratory condition
High concentrations can cause serious illness, unconsciousness and death. Lower-level exposure over a longer period can also make somebody unwell.
What Are the Symptoms of Carbon Monoxide Poisoning?
Carbon monoxide poisoning can feel similar to the flu, food poisoning or general tiredness. Common symptoms include:
- headaches
- dizziness
- nausea or vomiting
- weakness or unusual tiredness
- confusion
- chest or muscle pain
- shortness of breath
- changes to your vision
Severe exposure may cause breathing problems, loss of consciousness or collapse.
Please note: WarmZilla is not a medical provider, so this information should not replace professional medical advice. You can find the full list of symptoms in the NHS guidance on carbon monoxide poisoning.
Symptoms may become worse while you remain inside the affected property. Move into fresh air and seek medical advice if you think carbon monoxide exposure may be involved.
How Can You Tell the Difference Between Carbon Monoxide Poisoning and Flu?
Carbon monoxide poisoning can resemble flu or food poisoning because it may cause headaches, nausea, weakness and tiredness.
However, these clues could suggest that carbon monoxide is involved:
| Possible clue | Why it matters |
|---|---|
| Do you not have a high temperature? | Flu and other infections often cause a fever, while carbon monoxide poisoning usually does not. |
| Are several people feeling unwell at the same time? | Shared symptoms may point to something inside the property rather than an infection. |
| Are your pets also becoming unwell? | Animals can also be affected by carbon monoxide exposure. |
| Can you tell if the symptoms worsen inside the property? | This may indicate an indoor source of carbon monoxide. |
| Do you feel better after going outside? | Government guidance notes that symptoms often improve once someone is removed from the source. |
| Do your symptoms return when you go back inside? | Symptoms linked to a particular building or room should be taken seriously. |
| Have you used a boiler, fire or other fuel-burning appliance recently? | Faulty or poorly ventilated appliances can produce carbon monoxide. |
You can read more in the NHS guidance on carbon monoxide poisoning and the UK government’s carbon monoxide guidance.
These clues cannot confirm carbon monoxide poisoning and should never replace a working alarm or professional medical advice.
After all, carbon monoxide has no colour, smell or taste, so you cannot reliably detect it yourself.
An Engineer’s View
Carbon monoxide has no colour, smell, or taste, making it an invisible threat if your heating system isn’t functioning properly. Annual servicing is the only guaranteed way to ensure your boiler is combusting fuel safely and your flue is completely clear.
– Matthew Powell, Engineer
What Causes Carbon Monoxide in the Home?
Carbon monoxide is usually connected to a problem with combustion, ventilation or the route used to remove exhaust gases.
Common causes include:
Poorly Maintained Appliances
A boiler, fire or heater that has not been serviced may no longer burn fuel safely.
Internal components can become dirty, damaged or incorrectly adjusted. Regular boiler servicing can help identify developing problems before they become dangerous.
Blocked Or Damaged Flues
A flue carries combustion gases away from the appliance and out of the property.
Bird nests, debris, structural damage or poor installation can prevent these gases from escaping safely. There are signs that UK homeowners can look for to tell when their boiler’s flue is blocked.
Inadequate Ventilation
Fuel-burning appliances need an adequate supply of air.
Covering ventilation grilles, blocking air bricks or using equipment in an enclosed room can interfere with combustion and allow fumes to accumulate.
Incorrect Appliance Installation
Gas work carried out by somebody who is not properly qualified can leave an appliance, connection or flue in an unsafe condition.
Gas appliances should only be installed, repaired or serviced by an engineer who is registered and appropriately qualified for that type of work.
Using Outdoor Equipment Indoors
Barbecues, camping stoves and petrol generators should not be used inside homes, tents, garages or other enclosed areas.
Opening a door or window does not necessarily provide enough ventilation to make this safe.
Petrol-powered equipment can produce dangerous levels of carbon monoxide within a short period when used in an enclosed space.
Boiler Finance Calculator
Price of BoilerFinance available on all orders between £1,000 and £25,000
£740.00
Select a Representive Example:
Affordable
Mid - Range
Premium
Please note the above quotation is an indicative cost and actual monthly payments may vary by +/- 2p per month. Only available to UK residents over 18, subject to terms and conditions. To apply for finance, please add the product to your cart, proceed through checkout and select 'Apply For Finance' as your payment option where you can complete the application form online. Credit is provided by Novuna Personal Finance, a trading style of Mitsubishi HC Capital UK PLC, authorised and regulated by the Financial Conduct Authority. Financial Services Register no. 704348. The register can be accessed through http://www.fca.org.uk
What Are The Signs of A Carbon Monoxide Leak?
Carbon monoxide itself does not create visible stains, condensation or coloured flames.
However, problems with an appliance may leave warning signs.
Possible signs include:
- yellow or orange flames instead of a crisp blue flame
- soot or dark staining around the appliance
- a pilot light that repeatedly goes out
- increased condensation near the appliance
- unusual smells or fumes coming from the appliance, although carbon monoxide itself has no smell
- visible damage to a flue
- difficulty lighting the appliance
- the appliance regularly shutting down
- several people feeling unwell in the same room
Some modern appliances may operate differently, so flame colour alone cannot confirm whether an appliance is safe.
Do not wait for visible warning signs. A faulty appliance can produce carbon monoxide without leaving obvious marks.
How Can You Prevent Carbon Monoxide Poisoning?
No single precaution can remove every risk. The safest approach combines regular maintenance, correct appliance use and suitable alarms.
Service Your Boiler Regularly
Have your gas boiler and its flue checked by a Gas Safe registered engineer.
The Health and Safety Executive strongly advises homeowners to have gas appliances and flues safety-checked at least once every 12 months.
Oil, wood and solid-fuel appliances should also be maintained by a competent professional.
Keep Flues and Chimneys Clear
Have chimneys swept as recommended for the appliance and fuel being used.
Do not block flues, ventilation grilles or air bricks. These features may form an essential part of the appliance’s ventilation system.
Use Appliances Correctly
Never use a gas hob or oven to heat a room.
Do not bring a lit barbecue indoors, even after cooking has finished. Charcoal can continue to produce carbon monoxide as it cools.
Portable generators and petrol-powered tools must be kept outside and safely away from doors, windows and ventilation openings.
Check Your Engineer
Gas engineers must be registered with the Gas Safe Register to carry out gas work legally in the UK.
Ask to see the engineer’s Gas Safe ID card and check that they are qualified to work on the appliance concerned.
Install Carbon Monoxide Alarms
Place carbon monoxide alarms in appropriate locations throughout the property.
Follow the alarm manufacturer’s installation instructions. Positioning requirements can vary depending on the model and the room in which it is installed.
An alarm should not replace proper installation, servicing or maintenance. Gas Safe Register advises that alarms should not be treated as the only form of prevention.
Where Should You Install A Carbon Monoxide Alarm?
Install a carbon monoxide alarm in rooms containing fuel-burning appliances, such as a boiler, fire or stove. It is also sensible to place alarms near bedrooms and on each occupied floor, where they can be heard while people are sleeping.
You may also need alarms in caravans, boats or holiday accommodation that contain combustion appliances.
Always follow the manufacturer’s instructions, as the correct position can vary between models. Some alarms must be mounted on a wall or ceiling and kept away from windows, vents, cupboards or furniture that could restrict airflow.
Choose an audible alarm that meets the relevant British or European safety standard. Test it regularly and replace the batteries or the alarm itself when instructed.
Are Carbon Monoxide Alarms A Legal Requirement?
Carbon monoxide alarm requirements vary depending on the type of property and its location in the UK.
In England, landlords must provide a carbon monoxide alarm in every room used as living accommodation that contains a fixed combustion appliance. Gas cookers are excluded from this particular requirement.
Landlords must also repair or replace an alarm once they have been informed that it is faulty and the fault has been confirmed. These rules have applied since 1 October 2022 under the Smoke and Carbon Monoxide Alarm Regulations for England.
Different requirements apply elsewhere in the UK. Homeowners, landlords and tenants can check the relevant official guidance for Scotland, Wales and Northern Ireland.
Even where an alarm is not legally required, installing one can provide an important additional layer of protection.
What Should You Do When A Carbon Monoxide Alarm Sounds?
- Treat every alarm as genuine.
- Stop using fuel-burning appliances if it is safe to do so.
- Open doors and windows on your way out if this does not delay your escape.
- Get everyone, including pets, into fresh air.
- Call the National Gas Emergency Service on 0800 111 999 when gas could be involved.
- Seek medical help if anyone has symptoms.
- Do not use the appliance again until it has been declared safe.
- Do not remove the batteries, silence the alarm and remain inside.
Carbon monoxide levels may fluctuate. The fact that an alarm stops sounding does not prove that the danger has passed.
How Is Carbon Monoxide Poisoning Treated?
Carbon monoxide poisoning requires medical assessment.
Doctors may ask about:
- the symptoms
- the suspected source
- how long the exposure lasted
- whether other people became unwell
- whether symptoms improved outside
- whether an alarm activated
A blood test may be used to measure carboxyhaemoglobin levels.
Jargon Buster: Carboxyhaemoglobin
A harmful compound formed in the blood when carbon monoxide is inhaled and binds to haemoglobin, preventing the normal transport of oxygen to the brain and vital organs.
Treatment usually involves moving the patient away from the source and providing oxygen. More serious cases may require hospital treatment and specialist care.
Do not delay seeking help while attempting to identify the appliance yourself.
Can a New Boiler Reduce the Risk of Carbon Monoxide?
Replacing an old, damaged or unreliable boiler can remove a potential source of carbon monoxide. However, every new boiler must still be installed correctly, serviced regularly and used alongside a suitable carbon monoxide alarm.
Modern boilers include safety controls that can shut the appliance down when certain faults are detected. A boiler that repeatedly locks out, produces unusual smells, or leaves stains around the appliance should still be inspected by a Gas Safe registered engineer rather than continually being reset.
When a boiler is no longer safe or economical to repair, arranging a replacement can be simpler than many homeowners expect.
WarmZilla’s online boiler survey asks a few straightforward questions about your home before showing you suitable boiler options and fixed prices. You can then compare the available models, choose your boiler and arrange the installation online.
A new boiler does not replace regular servicing or carbon monoxide alarms, but professional installation and ongoing maintenance can help keep your heating system operating safely.
Frequently Asked Questions
Can You Smell Carbon Monoxide?
No. Carbon monoxide has no smell, colour or taste. A working carbon monoxide alarm is needed to warn you when dangerous levels are detected.
Does Opening A Window Stop Carbon Monoxide Poisoning?
Opening windows may help ventilate the room, but it does not make a faulty appliance safe. Leave the property and have the suspected source checked before using it again.
Can A Boiler Leak Carbon Monoxide When It Is Switched Off?
A boiler that is completely switched off should not be burning fuel. However, carbon monoxide may remain in the property after the appliance stops, and another appliance could be responsible. Leave the building and obtain professional advice when an alarm sounds.
Have a question? Please contact us on Live Chat
About the Author