Many people have boiler flues that go up into the loft and are therefore out of sight and out of mind. As gas engineers it’s our duty to inspect these flues even though they might be in an inconvenient place.

We quite often find that other gas engineers haven’t been up to check the condition of these flues and sometimes find that they haven’t been installed correctly in the first place.

At a recent job in North Shields we found a long flue that could have had a poor fall, i.e. a gradient to allow any condensate water to trickle back into the boiler and out of the condensate waste pipework. The main length of the flue looked fine with over 150mm of fall over a 3m length which was in excess of the 79mm specified by the manufacturers instructions. However the shorter length that turned to meet the boiler’s vertical flue was fitted horizontally resulting in condensate water pooling and then eating through the seals as its slightly acidic.

[Chemistry Lesson 1 – condensate water is a mixture of water (H₂O) and Carbon Dioxide (CO₂), combining the two creates Carbonic Acid – (H₂O + CO₂ = H₂C0₃) which is the chemical that eats away at the seals.]

These damaged flue parts needed to be replaced as this system is “At Risk” of becoming a serious problem as the exhaust gases follow the condensate water and enter the boiler to take part in the combustion process again, creating Carbon Monoxide. The corroded water entered the boiler and caused further corrosion to the steel parts within the boiler as well as dripping through the boiler onto the contents of the airing cupboard.

[Chemistry Lesson 2 – Carbon Dioxide (CO₂) and Air comprising of 23% Oxygen (O₂) and Natural Gas (Methane CH₄) react in the combustion chamber to create Carbon Dioxide CO₂, Water Vapour (H₂O) and Carbon Monoxide – O + CO₂ + CH₄ = H₂0 + CO + CO₂ ]. Carbon Monoxide or CO is a very dangerous gas as it has a similar density air and so floats in the atmosphere where it can be breathed in by humans. excessive amounts of CO can cause vomiting, brain damage, paralysis and death.

The faulty pipework was rectified by Macoun which entailed replacing 4 parts of the system at considerable expense to the customer, all because a small length of flue was installed incorrectly. The laser line is a level line. The flue was also properly hangered to prevent it coming loose, another common problem found in lofts.

If you suspect you have a level flue it would be best to have your regular service engineer look at it and report back, or alternatively we can look at it for you.