Do boilers emit carbon monoxide?

What is carbon monoxide?

Carbon monoxide is produced when your appliance isn’t burning its fuel correctly. It occurs when there isn’t enough oxygen for the gas to burn completely, resulting in carbon monoxide being formed as a waste product. Boilers can produce carbon monoxide naturally, but the gas is usually carried out of your house via a flue. If your  flue is blocked, the carbon monoxide has nowhere to go and will escape into your home. Carbon monoxide can also be present as a result of a leak in your appliance.

Carbon monoxide is odourless and colourless so it can be difficult to detect in your home. You should look out for common carbon monoxide poisoning symptoms. These could include:

• Breathlessness
• Loss of consciousness
• Headaches
• Dizziness
• Nausea

These symptoms are caused by a lack of oxygen in the brain. If you’re breathing in carbon monoxide for a long period of time, your oxygen levels could drop, which is why breathlessness and fainting are common symptoms. You may find that you feel ill at home but are much better when you’re out of the house.

If you suspect that you have a  carbon monoxide leak, you should open all of your doors and windows, turn off any gas appliances and leave the house. You should make a doctor’s appointment as soon as possible and organise for a Gas Safe registered engineer to come and survey your home.  

How to check for a carbon monoxide leak

There are some tell-tale signs that you may notice around the house if your boiler is leaking carbon monoxide. You may find that the gas flame on your stove burns yellow instead of blue. You should also look out for condensation on the inside of your windows or soot/staining around gas appliances.

Your boiler’s pilot light should be on all the time. If you find it’s blowing out frequently, you should call a suitably qualified heating engineer to check the boiler for you. Usually, the pilot light is unable to stay lit because there isn’t enough oxygen for the flame to burn, which is also the reason carbon monoxide is produced.

The most common reason for carbon monoxide poisoning in the home is faulty gas appliances. This doesn’t just include your boiler but also a gas cooker or gas fire. All of your appliances should be regularly checked and serviced by a Gas Safe registered engineer.

Can a boiler leak carbon monoxide when switched off?

Your boiler won’t be able to produce carbon monoxide when it’s switched off because it isn’t burning any fuel. However, if you think you may have a carbon monoxide leak, you should switch off your gas supply at the mains. At this stage, you may not know if it’s your boiler that’s leaking or another gas appliance. It’s safer to turn off all the gas and wait for a Gas Safe registered engineer to come to the house and determine the cause.

Can oil boilers produce carbon monoxide?

It isn’t just gas-burning appliances that produce carbon monoxide. It is the incomplete burning not just of gas, but of fuels in general. These fuels could include oil, wood and coal as well as gas. Therefore, an oil boiler could leak and produce carbon monoxide.

How to test boiler alarms

Every home should have a carbon monoxide alarm installed somewhere. They can save your life by reacting to the carbon monoxide in your home before you’ve even experienced any symptoms. Most carbon monoxide alarms will make a sound when they sense this gas, but some have screens that display a warning message. It’s much better to get one that makes a noise as this will wake you up in the night. A visual display alarm is good if you remember to check it regularly, but it cannot be checked when you’re asleep.

To test the alarm, there’s usually a button you can press, like on a smoke detector, that will sound the alarm. If the alarm sounds, it’s working correctly.

Some  boiler providers  may supply a carbon monoxide alarm with the purchase of your boiler. Even if they don’t, alarms are relatively cheap to buy and you will be able to purchase a reliable one for under £30.

You should place the alarm in an area between your gas appliances and your boiler. For example, if your boiler is in a downstairs bathroom and your gas cooker is in the kitchen, the hallway would be a good central location. The alarm should be placed at head height rather than on a ceiling so that you can check the batteries regularly.

The alarm shouldn’t be situated too near a gas appliance as it could mistakenly pick up the naturally occurring gases that are being expelled by the boiler and aren’t a danger to you.

If you are worried that you have a leak, you should call the  Gas Safe Register  on the following number during normal working hours: 0800 408 5500. You should also book an appointment as soon as possible with your GP, who will be able to perform a blood or breath test to check for carbon monoxide in your system.