4 sourced reports, with what to check before you buy. Each one links to the page it was reported on.
Costly or dangerous
QC45 earcup hinge breaks when replacing earpads
A repeat owner (second pair) reports the QC45's earcup hinge breaks under the physical manipulation needed to fit replacement earpads, and that the earpad retention tabs break too. The existence of aftermarket replacement headband-hinge parts for the QC45 (e.g. headsethut.co.uk listing 'Replacement Headband Hinge / End Caps' compatible with QC45) corroborates hinge cracking as a known failure point.
What to check. The QC45's hinge and earpad retention tabs are fragile; forcing replacement pads risks snapping the hinge where the cup meets the headband. Treat earpad replacement as delicate and expect the hinge to be a weak point.
A French Amazon customer review for the QC45 reports the pivot axis breaking after barely a month of use, and the review aggregate lists 'l'axe se brise' (the axis breaks) among durability complaints. This is an EU-market owner report of a mechanical pivot failure.
What to check. EU-market owners report the QC45's pivot axis can break early (within about a month); a broken pivot is a structural failure that typically requires repair or replacement.
QC45 power switch fails to boot the headphones (flashing power indicator, no startup sound)
Owner report on an iFixit repair forum describing their own QC45 that will not reliably power on: the power indicator flashes briefly and dimly, no startup sound plays, and the unit only boots roughly once every 20 tries. Contact cleaner on the switch did not fix it. This is a concrete electronic failure of the power switch/boot circuit, not a settings issue.
What to check. If a QC45 intermittently refuses to power on or shows a dim flashing power LED, the power switch/boot circuit is the suspect; this is not fixable by a reset and points toward hardware repair or replacement.
QC45 headband wiring insulation degrades inside the headband
The same repeat owner reports that, when opening the QC45, the insulation on the wires running through the headband to both earcups is breaking off. This is a wiring-durability concern that can lead to shorts or audio dropouts over time.
What to check. The QC45's internal headband wiring is reported to lose its insulation; this can cause intermittent audio or shorts and is not a user-serviceable fix.
These reports come from the pages linked under each item: owner forums, repair guides and workshops. They are not a diagnosis of any one unit, and a careful check of the one you are buying still applies.
Text from the Kriko Over-ear noise-cancelling headphones catalog, version 0.1.1, under the CC-BY-SA-4.0 license.
