This is a job I've finally got round to fixing, basically one of the double glazed units (sealed units) in our wood framed double gazed windows failed a while ago, by that I mean condensation was building up between the 2 panes of glass and rather than replace the whole frame i decided to just replace the sealed unit.
I found a company near to us who can make sealed units to whatever spec you want so I ordered one, much cheaper than replacing the whole frame.
The sealed units in upvc windows can also be replaced in a similar way and it's cheaper to replace them rather than the whole window frame, how to's can be found online and a few minutes searching will find companies near to you who can make replacement units, you will need measurements though.
