Are the window misting ? if so the seal around the outside of the unit has failed and is letting in air and or water. Usually caused by bad fitting or wrong type of glazing packers.
As Breezer said the only cure is to renew the double glazed unit.
There are company that repairs them by electric heat and re-sealed but not reliable.
Can you identify co(s) doing the heat and reseal type repair and say why they are unreliable. I would expect repair to be as reliable as origional manufactue (in Theory)
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