Flues leaking flue gasses anywhere over its length
Flues with heavy deposits of tar and other hydrocarbons either within the flue or on the external masonry
Flues and chimney breasts with staining and a build up of condensates
Open fires, stoves and otrher appliances that spill smoke causing odours and staining
Flues and chimney stacks that have undergone a chimney fire
Chimney stacks and flues with damaged, or poor, masonry
Stainless steel liners that have corroded and perforated.