The piezo mechanisms rarely fail. If you can see a spark, it's working. The problem is fuel delivery. Butane can be very hard to light in extreme cold or at high altitudes. Many times I've had butane BBQ lighters fail to light when in the mountains. You can carry a lighter in an inside pocket to keep the butane warm which helps a lot.
Coleman has sold bazillions of their 2 burner propane camp stoves with piezo lighters. Many of them won't light every time. You can see the spark so the piezo is working but the propane doesn't always get to the spark. I have yet to figure out why since any kind of other lighter will light it nicely. I have a couple of those long necked plasma lighters and keep one inside my stove for times when the piezo doesn't get it done.
