When you say shredded flue liner, @sandra_bennett59, are we talking about physical abrasion or chemical wear. Both can wreck a chimney fast, but the fix changes depending on the cause. Either way, it's a costly lesson in why you don't cut corners with fire safety.
Actually, thermal stress could be another factor to consider. Rapid heating and cooling might make the liner brittle over time. Idk, maybe it's just me, but that could add to the shredding without obvious abrasion or chemicals.