8 signs of a blocked chimney that you should not ignore

A blocked chimney is not just an annoying problem. It can be dangerous. Smoke that has no way out returns to the room. And with it comes carbon monoxide, which makes no noise and has no smell, yet it can kill.

Recognising warning signs is the first step towards safety. Here are eight situations when you should immediately contact a chimney sweep.

8 warning signs of a blocked chimney

• 1

  Smoke is entering the room.

  The most visible sign. If you see smoke in the room when flooding or lighting the fireplace, the chimney is either not drawing properly or is blocked. Immediately close the air supply and call a chimney sweep.

• 2

  Smell of exhaust fumes or tar without an apparent cause

  Do you smell an unpleasant odour of smoke or tar in the house even when not heating? This may indicate that the chimney is condensing or drawing air back from outside through deposited tar.

• 3

  The fire burns slowly or goes out on its own

  Fire requires air, and air enters via the flue. If the chimney does not draw well, the fire receives insufficient oxygen, burns slowly and may go out completely.

• 4

  Increased fuel consumption

  When a chimney does not draw optimally, combustion is incomplete, more fuel is consumed but less heat is produced. If you notice that you are using more wood or coal than before, it is time for an inspection.

• 5

  Condensate or moisture on walls near the chimney

  Wet spots or salt efflorescence on the wall near the chimney indicate that flue gases are condensing inside the flue and moisture has penetrated the masonry. A classic sign of a poorly functioning or oversized flue gas passage.

• 6

  Soot or ash on the doors of a stove or fireplace

  If soot or tar accumulates on the stove glass or doors, this indicates incomplete combustion and the chimney likely requires cleaning.

• 7

  Sounds from the chimney (whistling, cracking, movement)

  Sounds can have various causes, birds and other small animals often nest in chimneys, or there may be cracks caused by thermal expansion. Any unusual sound from a chimney is reason for an inspection.

• 8

  Unexpected headaches or nausea when heating is on

  This is the most serious symptom. If you or other residents of the building experience headaches, nausea or fatigue while heating is on, it may be carbon monoxide poisoning. Immediately ventilate the area, leave the building and call an ambulance as well as a chimney sweep.

What is the first step to take?

If you notice symptoms 1–3 (smoke, odour, weak draft), the first thing to do is:

1. Stop heating: close the air supply to the fireplace.
2. Ventilate the room
3. Call a chimney sweep for an inspection and cleaning.
4. Do not operate until the chimney sweep has confirmed that the flue is clear.

In case of nausea or difficulty breathing, leave the building and call emergency services. Carbon monoxide is fatal and cannot be detected by the senses.

How to prevent chimney blockages?

Regular cleaning in accordance with statutory deadlines is essential: see article how often to clean a chimneyFor wood-burning stoves, twice a year; for gas, once a year. Regular cleaning minimises the risk of blockages and fulfils your legal obligation.