We have your normal flue tile and block chimney maybe 20 years old. The Buderus boiler using it is very efficient and that means low stack temperature. That seems to have have caused flue gases to condense around the thimble and there are cracks and one missing piece inside the thimble. I thought flue tile could take anything. Guess not. So I am being told the proper way to fix this is to get a SS liner installed in the chimney and it will be set. Comments?