Is your house Victorian? The problem with wood, especially soft wood, when the fire is not burning well creosote is created in the exhaust gases which deposits on the inside of the flue. When these deposits get wet sulphuric acid is created which attacks the lime mortar that bonds the bricks together in old houses. This is why wood stoves should have a metal flue pulled down the chimney. If the fire hasn?t been used for a while get it swept and get them to put a smoke bomb up it to check for leaks especially in the loft and between floors.