Out walking on Doris Day I noticed that a local Eriba parked on someone's drive was sporting a new and substantial rip in its fitted cover immediately over the gas fire chimney.
It was apparent that when the owners had fitted their cover, they had neither removed the flue capping (which has a sharp rim all around its top) nor had they protected it with padding. Abrasion of the fabric against the fitting had sliced through the cover material and the action of the wind had then enlarged what had started out as a small cut into a serious tear.
Having had this happen to me when I first used our cover a few years ago, I am now careful (a) to remove the flue capping and (b) to tape bubble wrap over the end of the pipe before installing the cover. Some people fit a tennis ball into the chimney instead but having tried this I have found bubble wrap to be a better solution.
If you do suffer damage to your cover, repairs are simple. Our Protec came with a spare piece of fabric (I used some to make the mover gaiters qv); just cut a piece to cover the tear with a generous overlap and glue it over the damaged portion using EvoStik contact adhesive. If you follow the instructions supplied with the glue carefully, this will result in a strong and permanent waterproof repair.