IMPORTANT: It is essential to upgrade an existing flue system when replacing an old boiler; flue temperatures on a modern boiler are considerably lower and will not heat the chimney, as a result, condensation will form and may penetrate brickwork or drain back into the boiler causing internal corrosion (on a non-condensing boiler). Existing flexible corrugated liners must also be replaced; they will not be twin-walled, condensation will penetrate the liner.
