[Why do precast flues cause you so many problems Anjme? ]
They were not designed, 40 years ago, with inset fires in mind.
Often the walls are plastered directly over the concrete flue blocks causing cracking in the wall.
The flue block depth is often very shallow, it does not always start at floor level which is required for most inset installations.
The builders often "forgot" to clean off the excess cement from inside the blocks as they were placed upon each other causing cement to ooze out inside the new flue and form cement obstructions.
Its not very often we see a flue in the loft as you describe, more often there is a pipe, usually old asbestos, cemented into the blocks in the loft and then exiting out through the roof. This is often the wrong size, the joints are damaged or there are tight bends in the system which obviously restricts the flue pull.
These are but a few problems we come across.
We always carry out a full flue inspection and loft inspection without fail on these old precast flues.
Good luck with sorting it out. I am in Leeds myself if you get really stuck, look up my profile. ( not allowed to post my web addy)
They were not designed, 40 years ago, with inset fires in mind.
Often the walls are plastered directly over the concrete flue blocks causing cracking in the wall.
The flue block depth is often very shallow, it does not always start at floor level which is required for most inset installations.
The builders often "forgot" to clean off the excess cement from inside the blocks as they were placed upon each other causing cement to ooze out inside the new flue and form cement obstructions.
Its not very often we see a flue in the loft as you describe, more often there is a pipe, usually old asbestos, cemented into the blocks in the loft and then exiting out through the roof. This is often the wrong size, the joints are damaged or there are tight bends in the system which obviously restricts the flue pull.
These are but a few problems we come across.
We always carry out a full flue inspection and loft inspection without fail on these old precast flues.
Good luck with sorting it out. I am in Leeds myself if you get really stuck, look up my profile. ( not allowed to post my web addy)