As the RNLI themselves say:

Your lifejacket may save your life one day, but only if you maintain it properly. If your lifejacket is faulty, all you’re wearing is a dead weight.

At a RNLI lifejacket clinic, specially trained RNLI volunteers will show you how to maintain your lifejacket to keep it fully functioning. They’ll show you how to check it for wear and tear and do simple maintenance tasks like replacing gas bottles and firing heads. At one of their recent clinics, they found 80% of lifejackets had faults, and many had serious defects.

Don’t wait till you’re in trouble to find out your lifejacket is not working properly.