The cord on my Velux blackout blind wore through plastic runners of the blinds. The problem only became apparent after 4-5 years when the cord frayed on the sharp edges and jammed the blind.
Velux are saying I'm out of the 3-year warranty (the blind is about 5 years old). I'm saying that the blind was never fit for purpose as the plastic has clearly worn gradually from the time the blind was installed.
As well as opinions on whether I have a case, I'd be interested if people could check any blackout blinds they have for similar issues. It's a bit tricky to see as you have to look from the outside of the window!
The attached photo shows the two cords (one damaged) emerging from the end of the aluminium strip that runs across the bottom of the blind material. The worn groove can clearly be seen where the cord used to run. At the other end of the strip, the plastic wore all the way through and the cord snagged and broke on the aluminium.
It would have been a relatively cheap and easy repair if the problem had been spotted before the plastic wore all the way through, so worth a look if you have a Velux blind. A replacement is going to cost me £120 - they're not cheap!