Eldfast Ceramic Chimney Flue Re-lining from The Open Fire Centre, Oldham, Lancashire

This illustration shows a typical example of a chimney in need of flue re-lining. Smoke can be seen coming out of more than one flue outlet. There is smoke coming out through the pointing on the side of the chimney, a wisp of smoke is creeping round the lead flashing and a plume is rising from the roof tiles behind the chimney. This shows that the mortar sealing the chimney flue has perished and the mortar in the brickwork, "feathers", sealing one flue from another has also perished.
	The illustration left, shows how flue gasses can cross from the working flue through leaking feathers to another flue, probably a bedroom flue. With the right circumstances, the carbon monoxide laden flue gasses can be drawn back down into the bedroom with fatal consequences. It must be stressed that contrary to popular belief, solid fuel creates more carbon monoxide than gas fires so it is vital that the flue is sound.
The chimney flue, shown right, is a real example of a flue in need of re-lining. It can clearly be seen that the mortar between the bricks has been eaten away, allowing flue gasses to escape. This is a chemical reaction between the acid-laden flue gasses and the alcaline mortar and if left unchecked, will result in the bricks becoming unstable.