The first useful question about condensation is simple: which surface is wet? Moisture on the room side, outside face or inside an insulating glass unit can point towards different conditions.
Record before diagnosing
Photograph the affected pane, note the time and weather, and confirm the location of the moisture. Ask whether it clears as conditions change. For room-side condensation, record indoor humidity, temperature and ventilation conditions. Moisture between the panes warrants investigation of the unit rather than an assumption that the room merely needs more ventilation.
Avoid a single-cause answer
External condensation can occur on thermally efficient glazing when the outside glass surface falls below the dew point of the surrounding air. It is not automatically evidence of a defective unit. Equally, that observation does not explain every reported patch of moisture.
A short inspection log can prevent unnecessary replacements: pane reference, surface, timing, surrounding conditions and photographs. Compare repeated observations before deciding on corrective work. The diagnosis should account for the window, its surroundings and how the room is operated, rather than relying only on the glass product name.
Reference and further reading
Pilkington: Top tips for installers on window condensation.
General educational guidance. Use current local requirements, product-specific evidence and competent project assessment for design and construction decisions.