Crack in clay tile above the roof line -- how serious? can it be repaired? easily replaced?

[EdAK]

I just had my fireplace (fireplace with glass doors and "grate heater") cleaned. the Chimney sweep company said that the second tile down from the top had a rather large crack in it and that the only way to repair it was to reline the chimney. I'd been through
this before and I had checked with a different company who had told me that since the crack was "above the roof line", it was still safe. I am wondering if: 1. can the cracked tile be replaced without dismantling the chimney - which the company implied would be
necessary to replace the cracked tile; 2. could I just smear furnace cement over the crack to seal it?
Thanks for any help/advice.
Ed

 

[bigburner]

If you can reach it, using refractory cement should do the trick or a ramming plastic {it's refractory-not plastic}, if you are building a flue and midier any flues or even a straight stack. refractory cement is the recommended joint procedure. If the chimney is build correctly you should be able to remove the concrete cap and pull up the flues also as they should have expansion clearance around them. If there are several broken ones just go for the liner.