It is an amazing fact that uPVC double glazing was sold by the industry as a maintenance free product. While it is true the uPVC frame will last approximately 10,000 years before degrading, the mild steal and cast Zink moving hardware parts will last an average of 10 years before they start to fail.The problem with window company guarantees:i) Many window companies have gone out of business leaving the guarantees worthless,ii) Most guarantees last about 10 years so end just when you need them,ii.