It is an essential requirement when installing a gas or multi-fuel appliance to have your chimney swept by a competent sweep. The importance of having your flue swept cannot be over emphasised. If you don't have your chimney swept or smoke tested problems may not be detected such as blocked flues, birds nests etc…
Flexible stainless steel flue liners are often required for gas and multi-fuel appliances. All properties could require lining but they are generally fitted to older properties (over 60 years old).
When the appliance that is serving the flue is used continually for a long period, the hot gasses, tars and acids eats into the chimney walls and erodes the mortar joints. The result is dangerous/fatal fumes leaking into the the rooms above.
The flue liner is installed from the top then sealed at the top and bottom, basically creating a new chimney.
If your chimney requires a flue liner for either gas or muli fuel it is imperative that you choose a Gas Safe approved company to install your liner, Wilsons are that company. Reccomended for many years by numerous fireplace outlets accross Merseyside. Wilsons have an unparalled reputation for service, quality and reliability.
Wilsons offer a wide range of cowls and bird-guards. They are strongly advised to prevent the entry of birds and weather into the chimney. If you live near trees flues can also be blocked with leaves, nests etc...
The smoke test is probably the most important aspect of having your flue checked. Once it has been determined that your flue is clear (by sweeping), the smoke test is required to ensure that there is no leakage of fumes to rooms above or neighbours' property.
Obviously if this was to occur it is extremely dangerous and can only be rectified by having your chimney lined.