A carbon monoxide (CO) alarm is a simple yet essential component of any home, and it’s often overlooked. But do you know how to test it properly? Knowing how to check that your alarm is working correctly could be the difference between life and death. Read on for expert advice that could save your life.
Quick answer: how do you test a carbon monoxide alarm?
- Press and hold the test button until the alarm sounds.
- Listen for the correct alarm pattern.
- Replace the batteries if the alarm is weak, silent, or showing a low-battery warning.
- Check the alarm date, expiry date, and position.
- Test monthly and after every battery change.
- Do not test a carbon monoxide detector with a candle, match, smoke, car exhaust, gas hob, boiler flue, or any improvised combustion source.
- If the alarm sounds when you are not testing it, treat it as a real carbon monoxide warning and leave the property.
- If anyone feels unwell, has collapsed, has chest pain, or is struggling to breathe, call 999 immediately.
What is a Carbon Monoxide Detector?
A carbon monoxide detector should be installed in every home or business that burns gas as fuel. Carbon monoxide is an invisible, odourless, and colourless gas that’s incredibly dangerous. If left undetected, it can be fatal. It binds with red blood cells in your body, depriving your lungs of oxygen, which can lead to severe health consequences or even death.
Early symptoms of carbon monoxide poisoning include headaches, nausea, dizziness, confusion, and shortness of breath. But it’s far safer, and easier, to prevent this danger with the right safety measures. Installing and regularly testing your carbon monoxide detector is a simple and affordable way to protect your loved ones.
If you don’t have a CO detector yet, and your home uses gas appliances like central heating, cooking hobs, or water heaters, install one now! CO alarms are available at most DIY stores and online.
A carbon monoxide detector is designed to warn you if CO may be present, but it does not replace regular servicing or safety checks for boilers and other fuel-burning appliances.
For homeowners, an annual boiler service is one of the most practical ways to reduce the risk of unsafe boiler operation.
If you are a landlord, keeping gas appliances checked and maintaining working alarms should sit alongside your annual gas safety responsibilities.
You can read more about gas safety certificates if you manage or let a property.
Need help installing your detector? Call us at 0203 807 5817, and one of our fully qualified Gas Safe registered engineers will assess your property and install detectors at the correct locations, near each fuel-burning appliance.
Step-by-Step: How to Test Your Carbon Monoxide Alarm
Testing your carbon monoxide detector is vital to ensure it’s working and ready to protect your home. Follow these steps to ensure your detector is functioning properly:
- Read the manufacturer’s instructions.
Different carbon monoxide alarms can have different button positions, beep patterns, battery warnings, and replacement dates.
Always check the manufacturer’s instructions for your exact model. - Check the Placement:
Ensure the detector is placed at least 1 metre away from any fuel-burning appliance (like gas boilers, fires, or stoves) and ideally 1½ metres from the floor. Since carbon monoxide is lighter than air, it accumulates in the warmer air near the ceiling.
Make sure the alarm is not hidden behind furniture, covered by curtains, painted over, or blocked by household items. - Test the Alarm:
Most carbon monoxide detectors feature a test button. Push the button, and you should hear a series of four beeps followed by a brief pause. This confirms that the alarm is functioning. It is important to test your carbon monoxide detector regularly so you know it is working when you need it most.
Press and hold the test button until the alarm sounds, unless your manufacturer’s instructions say otherwise. - Listen for the correct beep or alarm pattern.
Many alarms sound in a repeated pattern, while others may have model-specific alerts.
If the alarm sound is weak, distorted, intermittent, or silent, treat it as a sign that the unit or batteries may need attention. - No Beeps?
If you don’t hear any beeps after pressing the test button, press it again. If there’s still no sound, the detector may be malfunctioning. - Replace the Battery:
If the detector emits a low battery warning beep, it’s time to replace the battery. If it still doesn’t work after changing the battery, the device may need to be replaced. - Check the expiry or replacement date.
Carbon monoxide alarms do not last forever.
If your alarm is past its expiry date, replace it even if the test button still makes a sound. - Regular Testing:
It’s important to test your CO alarm monthly to ensure it’s functioning properly, so it’s always ready to protect you.
Test again after every battery change. - Test every alarm in the property separately.
If you have more than one carbon monoxide alarm, press the test button on each unit rather than assuming all alarms are working. - Make sure vulnerable occupants know what the alarm sounds like.
Children, older people, tenants, and anyone with mobility or health concerns should know what the alarm means and what to do if it sounds.
Important: the test button checks the alarm sounder and electronics. It does not test whether carbon monoxide is present in the room at that moment.
If you are worried about a boiler, gas fire, hob, flue, or ventilation issue, arrange a proper appliance check by a qualified professional.
Should You Test a Carbon Monoxide Detector With a Candle?
No. You should not test a carbon monoxide detector with a candle.
While some may suggest using a candle to test your carbon monoxide alarm, this is not recommended. Lighting a candle near the detector may expose you to unnecessary risks and doesn’t guarantee an accurate test. The test button on your device is designed to accurately verify its functionality, ensuring both safety and reliability. Always use the test button for an accurate and safe check.
You should not test a carbon monoxide alarm using:
- A candle
- A match
- A cigarette
- Car exhaust
- A boiler flue
- A gas hob
- Smoke from burning paper
- Any improvised combustion source
A candle may create smoke and heat, but smoke does not prove the carbon monoxide sensor works.
A carbon monoxide detector is not the same as a smoke alarm.
DIY testing can create fire risk, carbon monoxide exposure, alarm damage, or false confidence.
Car exhaust, boiler flues, and gas hobs are especially dangerous and should never be used to test a home alarm.
Some professionals may use calibrated equipment or manufacturer-approved test gas, but this is not a DIY home test.
The safe household test is the built-in test button.
If you are concerned that an appliance may be producing carbon monoxide, do not try to recreate the issue yourself. Turn the appliance off if safe, get fresh air, and arrange a Gas Safe registered inspection before using it again.
Can You Test for Carbon Monoxide Without a Detector?
No. You cannot reliably test for carbon monoxide at home without a working carbon monoxide alarm or professional testing equipment.
Carbon monoxide has:
- No smell
- No taste
- No colour
- No visible warning sign
You must not rely on:
- Symptoms alone
- Flame colour
- Smells
- Condensation
- Pets behaving strangely
- DIY tricks
- Candles or matches
- Smoke
- Gas hobs, boiler flues, or car exhaust
To reduce the risk of carbon monoxide exposure at home:
- Fit a certified carbon monoxide alarm.
- Test monthly using the test button.
- Replace batteries and expired alarms promptly.
- Keep boilers and fuel-burning appliances serviced.
- Use a Gas Safe registered engineer for gas appliance concerns.
- If a leak is suspected, get everyone into fresh air.
- If anyone is unwell, call 999.
- If gas appliances may be involved, call the National Gas Emergency Service on 0800 111 999.
For South London homes, Aren Heating & Plumbing can help with gas appliance checks and advice on suitable carbon monoxide alarm placement.
How to Spot Carbon Monoxide Poisoning at Home
You cannot properly “test” for carbon monoxide poisoning at home without medical help. What you can do is recognise the warning signs and act quickly.
Early symptoms of carbon monoxide poisoning include headaches, nausea, dizziness, confusion, and shortness of breath.
Warning signs of carbon monoxide poisoning can include:
- Headache
- Dizziness
- Nausea
- Vomiting
- Tiredness or weakness
- Confusion
- Chest pain
- Shortness of breath
- Collapse
- Symptoms that improve when leaving the property
Symptoms may affect more than one person at the same time.
CO poisoning can feel like flu, food poisoning, tiredness, or a hangover.
Babies, older people, pregnant women, and people with heart or breathing conditions may be at higher risk.
If you suspect carbon monoxide poisoning:
- Get everyone outside into fresh air immediately.
- Do not use electrical switches or naked flames if gas is suspected.
- Call 999 if anyone feels unwell, has collapsed, has chest pain, or is struggling to breathe.
- Call the National Gas Emergency Service on 0800 111 999 if gas appliances may be involved.
- Do not use the appliance again until it has been checked by a Gas Safe registered engineer.
If you live in South London and the immediate emergency has been handled, Aren Heating & Plumbing can arrange a gas appliance or boiler safety check before you use the appliance again.
How to Check for Carbon Monoxide in Your Home
The only reliable way to check for carbon monoxide in your home is through a carbon monoxide alarm. If you suspect a CO leak or your detector sounds, don’t hesitate to act.
You cannot see, smell, or taste carbon monoxide.
A working CO alarm is the only reliable domestic warning method.
Engineers use appropriate testing equipment for appliances, flues, combustion, and ventilation.
A domestic alarm is essential, but not a substitute for proper servicing.
Common carbon monoxide risk sources include:
- Gas boilers
- Gas hobs
- Gas fires
- Open fires
- Wood burners
- Blocked or damaged flues
- Poor ventilation
- Badly maintained appliances
- Incorrectly installed heating equipment
Signs of Carbon Monoxide Poisoning:
- Headaches
- Nausea and dizziness
- Confusion or shortness of breath
If anyone is showing symptoms of poisoning, immediately evacuate the building and contact emergency services. Carbon monoxide can be life-threatening, which is why detection and prevention are essential. Regular appliance checks, gas safety certificates, and inspections by qualified professionals all play an important role in keeping your property safe.
To reduce the risk of carbon monoxide in your home:
- Test each carbon monoxide alarm monthly.
- Replace expired alarms.
- Keep vents clear.
- Do not block air bricks or ventilation grilles.
- Have fuel-burning appliances serviced regularly.
- Use a Gas Safe registered engineer for gas work.
- Check that alarms are not covered, painted over, removed, or left without batteries.
- Make alarm testing part of your autumn and winter heating safety routine.
For homeowners, an annual boiler service is one of the most practical ways to reduce the risk of unsafe boiler operation.
If you are a landlord, read more about gas safety certificates.
If you are buying a property, a home buyers heating and plumbing survey in South London can help identify visible concerns before they become costly or unsafe problems.
What to Do If the Carbon Monoxide Alarm Goes Off (Not During Testing)
If your carbon monoxide alarm goes off, don’t panic, act quickly! The detector is warning you of a dangerous build-up of carbon monoxide in your home. Follow these steps immediately:
- Evacuate:
Get everyone out of the house, including pets. Move to fresh air outside. - Open doors and windows only if safe on the way out.
Do not put yourself at risk by delaying your exit. - Turn appliances off only if safe.
Do not spend time investigating the appliance if people are at risk. - Check for Symptoms:
Assess if anyone is showing signs of carbon monoxide poisoning, such as headache, dizziness, nausea, or confusion. - Call Emergency Services:
If anyone has symptoms of poisoning, call emergency services immediately. If no one is showing symptoms, you should still contact professionals to inspect the source of the leak.
Call 999 if anyone feels unwell, has collapsed, has chest pain, or is struggling to breathe. - Call the National Gas Emergency Service on 0800 111 999 if gas appliances may be involved.
- Do not re-enter until it is safe.
- Book a Gas Safe registered engineer inspection before using appliances again.
Never remove the batteries to stop the sound and continue using the appliance.
If the alarm later appears to be faulty, replace it, but only after you have ruled out a real carbon monoxide risk.
Remember, carbon monoxide poisoning is a real threat, causing 60 deaths per year in the UK. Always treat an alarm seriously and act fast.
Why is Regular Testing So Important?
Testing your carbon monoxide alarm isn’t just a one-time task. It’s crucial to do so regularly, at least once a month, to ensure that your alarm is working properly. A faulty alarm is like having no alarm at all.
Regular testing is especially important before autumn and winter, when boilers, gas fires, and heating systems are used more often.
Key Benefits of Regular Testing:
- Protects Your Family: Ensure your detector is always ready to detect any potential CO leaks.
- Prevents Costs from Replacement: Spot issues early with regular checks so you can avoid costly emergency repairs.
- Peace of Mind: Testing regularly reduces the risk of false alarms, ensuring that your family is safe from carbon monoxide exposure at all times.
A working alarm gives you an early warning, but regular boiler servicing and prompt repair of appliance faults are still essential.
If your alarm has sounded, your boiler is overdue a service, or you are unsure whether a gas appliance is safe, contact Aren Heating & Plumbing for local South London support.
Carbon Monoxide Alarm Help in South London
Need a Carbon Monoxide Alarm or Installation Services?
If you don’t already have a carbon monoxide detector in your home, or you need help testing or installing one, we’re here to help.
- Installation: Call 0203 807 5817 for expert advice and fast installation services by a fully qualified Gas Safe engineer.
- Testing: Not sure if your detector is working? We can test and replace faulty alarms to ensure your home stays safe.
Aren Heating & Plumbing supports homeowners, landlords, tenants, and property buyers across South London with practical gas safety and heating advice.
We can help with carbon monoxide alarm placement guidance, boiler servicing, gas appliance checks, and safety-led next steps if your alarm has sounded.
If you need local help, call us at 0203 807 5817 or contact Aren Heating & Plumbing to arrange support from a fully qualified Gas Safe registered engineer.
Why Choose Us?
- Fully Qualified Gas Safe Engineers: With years of experience, we provide reliable, professional installation and testing.
- Comprehensive Safety Solutions: We offer a range of services to ensure your home is protected from carbon monoxide and other gas-related risks.
- Fast, Reliable Service: We understand how important it is to keep your home safe, so we provide fast and efficient service you can trust.
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FAQs
How do you test a carbon monoxide alarm?
Press and hold the test button until the alarm sounds, then listen for the correct beep or alarm pattern. If the alarm is silent, weak, past its expiry date, or still not working after a battery change, replace it.
How often should I test my carbon monoxide detector?
Test your carbon monoxide detector at least once a month and after every battery change. You should also check the expiry date regularly because CO alarms need replacing after a set lifespan.
Can I test a carbon monoxide detector with a candle?
No. Do not use a candle, match, smoke, gas hob, boiler flue, car exhaust, or any improvised combustion source to test a carbon monoxide detector. Use the built-in test button instead.
Can I check for carbon monoxide without a detector?
No, you cannot reliably check for carbon monoxide at home without a working carbon monoxide alarm or professional testing equipment. Carbon monoxide has no smell, taste, or colour, so a certified alarm is essential.
What should I do if my carbon monoxide alarm goes off?
Leave the property immediately, get everyone into fresh air, and call 999 if anyone feels unwell, has collapsed, has chest pain, or is struggling to breathe. If gas appliances may be involved, call the National Gas Emergency Service on 0800 111 999 and do not use the appliance again until it has been checked by a Gas Safe registered engineer.
Does the test button check for carbon monoxide in the room?
No. The test button checks the alarm sounder and electronics. It does not confirm whether carbon monoxide is currently present in the room.
Who can help with carbon monoxide alarm advice in South London?
Aren Heating & Plumbing can help South London homeowners, landlords, tenants, and property buyers with carbon monoxide alarm placement advice, boiler servicing, and gas appliance safety checks. Call us at 0203 807 5817 for local support.
