DIY Supermarket

The installation of a boiler that entails the discharge of combustion by-products into the existing chimney will involve fitting a flexible stainless steel flue liner; otherwise gases can condense on the flue walls and damage the brickwork.  Should condensation run back down the flue, this can cause boiler corrosion.

The liner works by trapping an insulating layer of air between it and the flue, and prevents condensation forming.  You have to make sure you use the correct type of liner, as there are different types for oil and gas boilers.

Solid fuel boilers preclude the use of flexible liners, and you have to line these by either using sectional liner or pumped-in lining of lightweight insulating material.

Drop a weighted string down the flue from the chimney first of all to measure the length of liner you will need. Then, chip the flaunching away from the stack and lift off the old chimney.  Drop the string down again to a helper at the other end and attach it to the plug-in nose cone, then start lowering the liner into the flue.  When it reaches the bottom, secure the top end in the clamping plate and fit a terminal cowl over its top.

Once the liner is securely in place you can remake the flaunching using sand mortar, sloping it for rainwater runoff.  At the bottom end, fit the blanking-off plate around the liner just above the boiler to create an insulated air column and connect the liner into the flue using fire cement to make an airtight joint.