I had a problem with one of the windows in my living room. The glass fogged up, and it got increasingly worse and mold started to form. I had no windows warranty as they were bought with the house.
Dan came in and showed me the faulty window seal and the bad window insulation.
They replaced the faulty pane and redid the insulation on the whole window group (3 windows) without charging me anything extra, which was very nice on their part.
The worked neatly and fast and my window hasn't fogged up since.