We have exactly the same problem. We have had new sash windows fitted in 2 bedrooms and now both windows are leaking and the the company who fitted them say they are too busy to even come and look at their work for several weeks. This company (it goes by several names, Sash King and Alexander Johnson and Sons - the guy we dealt with was called Jim Johnson 07958439282) may not even be responsible - it maybe freak weather linked to something else, but to hear they are too busy to come and check their work seems really poor after we paid them a small fortune for these windows. All the roofers are busy and it is really stressful. Meanwhile the internal damage just keeps getting worse and worse in newly decorated rooms.