Carbon monoxide (CO) is a poisonous gas that you can't see, smell or taste. Exposure to the gas can cause long-term damage or be fatal. Every year 40 people die from carbon monoxide in the UK, and 200 people are hospitalised. You can find more information below on how to protect yourself and your home from carbon monoxide poisoning, and what to do if there is a leak.

The warning signs

It's easy to spot signs that your gas or heating appliances are producing carbon monoxide. Danger signs can include:

  • Soft yellow flames
  • Sooty stains or discolouration on or around gas appliances
  • Increased levels of condensation in rooms with gas appliances
  • Fumes or smoke in the house
  • Slower than usual burning of solid fuel fires

What are the symptoms of carbon monoxide poisoning?

Symptoms can include:

  • Headaches
  • Drowsiness
  • Visual problems
  • Dry throat
  • Nausea
  • Vomiting

If you or someone you're with is feeling ill, visit your doctor urgently. Explain that symptoms may be related to CO poisoning and ask that they test a blood or breath sample.

If someone is seriously ill from poisoning it's vital that they leave the room and get fresh air. You should call for medical help urgently. Make sure that when help arrives you tell them that you suspect carbon monoxide poisoning. This will ensure they get the appropriate treatment quickly.

What to do if you detect possible carbon monoxide

If your carbon monoxide alarm sounds or you suspect a leak:

  • Stop using all appliances, switch them off, and open doors and windows to ventilate the property
  • Evacuate the property immediately – stay calm and avoid raising your heart rate
  • Call the National Gas Emergency Service on 0800 111 999 to report the incident, or the Health and Safety Executive (HSE) Gas Safety Advice Line on 0800 300 363
  • Seek immediate medical help – you may not realise you've been affected by the carbon monoxide, and going outside into fresh air won't treat any exposure by itself
  • Don't go back into the property – wait for advice from the emergency services

What causes carbon monoxide in the home?

Carbon monoxide is released into your home when faulty appliances start leaking. You must take the proper steps in your home to make sure you remain safe from carbon monoxide poisoning at all times.

It is also important to note that carbon monoxide poisoning is different to carbon dioxide poisoning. The safety steps to protect against carbon dioxide poisoning will also be different.

Where can I buy a CO detector?

All SSE engineers carry CO detectors, which are available to buy any time you've arranged for one to come to your home. You can also buy a detector online, or at a number of DIY stores and retail outlets. When you buy your detector, make sure it meets current European safety standards so that you know it'll work safely and correctly in your home.

Look for alarms marked with the ‘EN50291’ standard. This may be written as BSEN 50291 or EN50291 and with the 'CE' mark, which can usually be found on the packaging and product. Your alarm will also have either a Kitemark or Loss Prevention Certification Board (LPCB) logo to show independent testing and certification.

Positioning my carbon monoxide detector

When fitting your alarm, you should always follow the instructions that come with it. Where you put the alarm is important, so here are some tips for where to position it.

  • Alarms can be placed in rooms with fuel burning appliances (eg the room in or near where your boiler is kept).
  • Place the alarm at head height. This means it'll be at your breathing level. You don't have to fix the alarm to the wall to do this. It can be placed on a table or shelf.
  • If you have a portable battery alarm, you can place it in the room you spend most time in, or move it from room to room.
  • Don't place your alarm in a cupboard, behind furniture or near ventilation areas (eg extraction fans).
  • Keep your carbon monoxide alarm at least one metre away from fires, boilers, cookers or heaters.
  • Avoid placing your carbon monoxide alarm in areas near high condensation and steam (eg kettles, cooker tops, showers).


Always make sure to regularly test your carbon monoxide alarm, which you can do by using the test button. Check the instructions to see where the button is and how it works on your particular alarm. When the low battery signal sounds, you must either replace the batteries or buy a new carbon monoxide detector. To find out which, you can read the instruction manual that came with your detector.

Remember that your carbon monoxide alarm must never be used in place of annual safety checks. Contact a Gas Safe registered engineer every 12 months to ensure your appliances work correctly, remain in warranty and are safe to use.