Why misting appears between the panes
A double-glazed unit is manufactured as a sealed assembly. Once that seal no longer performs as intended, moisture can enter the cavity and visible condensation or haze can develop between the panes.
What gets replaced
The usual repair is the sealed glass unit rather than the whole uPVC frame, provided the frame, bead and surrounding components remain suitable. The replacement must be measured for the glazing system rather than simply ordering to the visible opening size.
Glass specification matters
Safety requirements, overall unit thickness, obscure patterns, decorative features and other glass details can affect what should be ordered. A survey should record these details before the replacement is manufactured.
Check the rest of the window at the same time
If the window is also difficult to close, draughty or has worn hinges, those are separate faults. A combined survey can record the glass and hardware so the quote covers the full repair rather than solving only the visible misting.
Multiple failed units
Where several panes have failed, each unit can be recorded by room and window position with its own measurements and photographs. That reduces confusion when the replacement units return to site.
Need someone to inspect the fault?
True Vision can turn the symptom into a measured repair scope and quote.