Its a bit of a tricky one asking the installers to come back as they are friends of the family. Not very good friends I hear you shout. Never the less it seems from the advice given that its a fairly straight forward task and if im honest id rather shell out a few quid and it hopefully rectify...
We have recently (December 2013) had our windows replaced as our old windows were showing signs of condensation and also looking pretty tired. We went for quite a high quality window frame and glazing as we wanted to ensure the temperature within the house was at a decent level all year round...