Blocked Flue Boiler

What happens if your boiler flue becomes blocked – what to do?

The flue of a boiler is an essential part of the home’s heating system. Fumes created by the boiler need to be able to escape into the outside air, and the flue is designed to help it do just that.
If the boiler flue becomes blocked. These fumes have nowhere to go other than the home. This is extremely dangerous and creates a situation that can become fatal incredibly quickly.
Carbon monoxide is normally released by the flue into the open air outside. When the flue is blocked and carbon monoxide builds inside the home, it only takes 15 minutes for the levels of the gas to become fatal. In England and Wales, according to the NHS, around 60 people each year are killed by carbon monoxide poisoning.

What can cause a flue to become blocked?

There are lots of ways that a flue can become blocked, such as:

• Leaves
• General debris
• dead birds
• Old birds’ nests

Pinecones and conkers can find their way in there too if the flue is vertical and there is an overhanging tree. These things, as well as other items, are allowed to build up the more the flue will become blocked. It is important to check and clear your boiler flue regularly.
Flues can either protrude through the roof, vertically or through a wall, horizontally. More often than not, the flue will be installed so that it exits a wall – this is usually the better option as most build-up causes are less likely to happen. That being said, these types of installations are more likely to become home to a bird’s nest at some point.
Covers can be purchased for either installation type, helping to cut down on blockages and the need to clear them as often.

What should you do if you think your flue is blocked?

If you suspect that your boiler flue may be blocked, turn off the boiler completely. Simply turning off the heating is not enough. The gas supply to the boiler has to be shut off. If you do not know how to do this, especially if you are not sure how to do it safely, then turn off the boiler and call a Gas Safe registered engineer. Explain the situation and they will happily send someone to you.
Should you believe that the flue may have been blocked for some time, you should check for the following symptoms that have been provided by the NHS. These symptoms of short-term exposure could be a signifier of carbon monoxide poisoning.

• Dizziness
• Feeling and being sick
• Tiredness and confusion
• Stomach pain
• Shortness of breath and difficulty breathing
• Difficulty concentrating
• Long-term exposure symptoms include:
• Mood swings and irritation
• Personality changes (intoxication)
• The feeling that everywhere is spinning (vertigo)
• Breathlessness and a heart rate of more than 100 beats per minute
• Muscle spasms or seizures
• Loss of consciousness

If any of the above have been or are being experienced, completely disable the boiler and seek medical advice from your GP.

Sealing a boiler flue

Your flue is required to be completely sealed. Any gaps around the edge of the flue raise the risk that gas can leak back into the home. Wherever the flue exits the home, either the roof or wall, it needs to be sealed on both sides – in and outside of the home.

If you are not sure if the flue is sealed correctly, you can ask a heating engineer to check for you. The engineer will normally conduct a test using smoke pellets. The device they use is held up to the seal, on the inside of the property. If the flue is not properly sealed, the smoke will be seen dissipating outside.

The health of you and your family is of the utmost importance, so making sure the flue is working correctly is crucial.
If you suspect that the flue may be blocked or not sealed properly, you need to call a qualified engineer to take a look as soon as is possible.

Quantum Gas Engineering Ltd. Are Accredited Viessmann installers.

Interested In Learning More? Contact Quantum Gas Engineering

For more information on Vaillant boiler installations in Primrose Hill, give Quantum Gas Engineering Ltd a call on 0203 633 2322 or email us at