A carbon monoxide (CO) alarm is a simple yet essential part of home safety, and it is often overlooked. Knowing how to check that your alarm is working correctly could be the difference between life and death.
Carbon monoxide is invisible, odourless, and colourless. It can come from faulty or poorly maintained boilers, gas cookers, gas fires, wood burners, water heaters, or other fuel-burning appliances.
If you are unsure whether your alarm, boiler, flue, or gas appliance is safe, test your CO alarm today and arrange a professional check. Aren Heating & Plumbing supports homeowners, landlords, tenants, and buyers across South London. Contact our team by phone, online form, or WhatsApp for practical advice.
How to Test a Carbon Monoxide Alarm: Quick Steps
To test a carbon monoxide alarm safely at home:
- Press and hold the test button until the alarm sounds.
- Listen for a loud, clear alarm tone.
- Check lights, display indicators, or app alerts if your model has them.
- Replace batteries if the alarm is weak, silent, or chirping.
- Check the expiry or replace-by date.
- Test monthly and after changing batteries.
- If you suspect carbon monoxide, leave the property, get fresh air, call the National Gas Emergency Service on 0800 111 999, and arrange a professional inspection.
The test button usually checks the sounder, battery, and circuit. It does not release carbon monoxide or prove that the sensor will detect gas in a real emergency.
What Is a Carbon Monoxide Detector?
A carbon monoxide detector should be installed in every home or business that uses gas, oil, coal, wood, or another fuel-burning appliance. Carbon monoxide affects the body’s ability to carry oxygen, which can lead to serious illness or death.
Early symptoms of carbon monoxide poisoning can include:
- Headaches
- Nausea
- Dizziness
- Confusion
- Shortness of breath
- Weakness
- Chest pain
- Unusual tiredness or sleepiness
Installing and regularly testing your carbon monoxide detector is a simple and affordable way to protect your home. Testing matters because batteries fail, alarms can be moved or damaged, fault lights can be missed, and sensors expire.
If you do not have a CO detector yet, and your home uses central heating, cooking hobs, gas fires, or water heaters, install one as soon as possible. Need help? Call Aren Heating & Plumbing on 0203 807 5822, and one of our qualified Gas Safe registered engineers can advise on suitable alarm locations near fuel-burning appliances.
A CO alarm supports home safety, but it does not replace regular boiler servicing, gas appliance checks, or gas safety inspections. For wider support, see our plumbing and heating services in South London.
How to Test Your Carbon Monoxide Alarm
Testing your carbon monoxide detector is vital to ensure it is working and ready to protect your home. Follow these steps to check your detector safely.
Check the Placement
Ensure the detector is fitted in line with the manufacturer’s instructions and UK safety guidance. In general, CO alarms should be placed near rooms with fuel-burning appliances such as gas boilers, gas fires, gas cookers, or stoves.
Do not hide alarms behind curtains or furniture. Avoid placing them too close to windows, vents, extractor fans, or humid areas unless the manufacturer’s instructions say otherwise.
If you are fitting a new gas cooker or reviewing appliance safety, our guide to gas cooker installation may help.
Test the Alarm
Most carbon monoxide detectors have a test button. Press and hold it, and you should hear a loud alarm sound, often a series of beeps depending on the model. This is the safest and most reliable routine home test.
The test button usually confirms that the sounder, battery or power supply, and basic electronic circuit are working. It does not normally test the sensor with real carbon monoxide or confirm that your home is free from gas.
No Beeps?
If you do not hear any beeps after pressing the test button, press it again and check the manufacturer’s instructions. If there is still no sound, the detector may be faulty.
If the alarm is chirping or showing a low battery warning, replace the battery where the model allows. If it still does not work, or if it is expired, damaged, or unreliable, replace the alarm promptly.
Regular Testing
Test your CO alarm at least once a month so it is always ready to protect you. You should also test it after changing batteries, when moving into a new home, before winter, and after boiler or gas appliance work.
Can I Test My Carbon Monoxide Detector With a Candle?
No. You should not test a carbon monoxide detector with a candle.
A candle does not provide a safe, controlled, or reliable carbon monoxide test. It can also create a fire risk, damage the alarm, contaminate the sensor, or give false confidence.
Always use the test button for routine checks and follow the manufacturer’s instructions.
How to Check for Carbon Monoxide in Your Home
The only reliable way to check for carbon monoxide in your home is with a working, in-date carbon monoxide alarm or professional testing equipment.
Possible warning signs linked to carbon monoxide or unsafe combustion can include:
- Headaches, nausea, dizziness, confusion, or shortness of breath
- Symptoms that improve when you leave the property
- A yellow, floppy, or unusual gas flame instead of a crisp blue flame
- Sooty or brown staining around appliances
- Excessive condensation
- Pilot lights frequently going out
- Poor appliance performance
- Pets appearing unusually sleepy, weak, or unwell
These signs are not proof that carbon monoxide is or is not present. If you suspect CO, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
What to Do If Your Carbon Monoxide Alarm Goes Off
If your carbon monoxide alarm goes off and it is not during testing, act quickly. The detector may be warning you of a dangerous build-up of carbon monoxide in your home.
- Get everyone out of the house, including pets, and move to fresh air.
- Open doors and windows on your way out if it is safe.
- Turn off gas appliances only if it is safe and quick to do so.
- Check whether anyone has symptoms such as headache, dizziness, nausea, confusion, weakness, chest pain, or breathlessness.
- Call the National Gas Emergency Service on 0800 111 999.
- If anyone feels unwell, seek urgent medical advice or call emergency services.
- Do not re-enter until you are told it is safe.
- Do not use the suspected appliance again until it has been inspected by a qualified professional.
Carbon monoxide poisoning is a real threat and causes deaths in the UK every year, so always treat an alarm seriously.
If your CO alarm has sounded, or you are worried about a boiler, gas cooker, or heating appliance in South London, contact Aren Heating & Plumbing after the immediate emergency steps have been followed.
Why Is Regular Testing So Important?
Testing your carbon monoxide alarm is not a one-time task. It is important to test it at least once a month to make sure the alarm is working properly. A faulty alarm is like having no alarm at all.
Key benefits of regular testing include:
- Protects your family: your detector is more likely to be ready to identify a potential CO leak.
- Spots problems early: regular checks help you identify weak batteries, fault warnings, or damaged alarms.
- Gives peace of mind: testing regularly helps you feel confident that your alarm is ready when needed.
When to Replace Your Carbon Monoxide Detector
Replace your carbon monoxide detector if it is expired, damaged, unreliable, or does not sound when tested.
A CO alarm can still make a sound when tested but have an ageing sensor, so always check the replace-by date.
Replace your CO alarm if:
- It has passed its expiry or replace-by date.
- The test button does not work.
- The alarm is damaged or missing parts.
- The fault indicator stays on after batteries are replaced.
- The manufacturer’s guidance says it should be replaced.
- You are unsure how old it is.
Carbon Monoxide Safety for South London Homes
South London has a mix of flats, period homes, conversions, rentals, and family houses, many of which rely heavily on heating during autumn and winter. Poorly maintained boilers, blocked flues, unsafe gas appliances, poor ventilation, or incorrect installation can all increase carbon monoxide risk.
If you are buying an older house or flat in South London, a home buyers heating and plumbing survey can help identify visible heating, plumbing, boiler, appliance, and safety concerns before completion.
Need a Carbon Monoxide Alarm or Installation Services?
If you do not already have a carbon monoxide detector in your home, or you need help testing, replacing, or installing one, we are here to help.
- Installation: call 0203 807 5822 for expert advice and installation support from a qualified Gas Safe engineer.
- Testing: not sure if your detector is working? We can advise on testing and replacement so your home stays safe.
- Gas safety support: if you are concerned about a boiler, gas cooker, or heating appliance, contact our team by phone, online form, or WhatsApp.
Why Choose Aren Heating & Plumbing?
- Fully qualified Gas Safe engineers with years of practical experience.
- Reliable, professional advice, testing, servicing, and inspection support.
- Comprehensive safety solutions for carbon monoxide and other gas-related risks.
- Fast, efficient service across South London.
- Support for homeowners, landlords, tenants, and buyers, especially during the busy autumn and winter heating season.
FAQ: Carbon Monoxide Alarm Testing
How do I test my carbon monoxide alarm?
Press and hold the test button until the alarm sounds. Listen for a loud, clear tone, check any lights or display indicators, replace batteries if needed, and check the expiry date. Test your CO alarm once a month.
Does pressing the test button mean there is no carbon monoxide?
No. Pressing the test button usually checks the sounder, battery, and circuit. It does not prove that the sensor can detect carbon monoxide gas or that the property is free from carbon monoxide.
Can I test a carbon monoxide detector with a candle?
No. Candle testing is unsafe and unreliable. It can create a fire risk, damage the alarm, contaminate the sensor, and give false confidence. Use the test button and follow the manufacturer’s instructions.
What should I do if my carbon monoxide alarm goes off?
Leave the property, get fresh air, call the National Gas Emergency Service on 0800 111 999, and seek urgent medical help if anyone feels unwell. Do not re-enter until you are told it is safe.
How often should I test or replace my carbon monoxide alarm?
Test it monthly, after changing batteries, before winter, when moving into a property, and after boiler or gas appliance work. Replace it if it is expired, damaged, unreliable, or does not sound when tested.
