Do you see mist or moisture between the two panes that no cloth can reach? Then your sealed unit has failed. The bad news up front: this cannot be solved with a trick. Below we explain why, and what you can do instead.
First: where is the condensation?
That is the key question, because there are three possibilities and only one of them is a fault.
- On the inside of the pane (in the room). Not a fault, this is a ventilation problem. Too much moisture in the house, too little air change. Airing more often, opening trickle vents and using an extractor hood usually solves it.
- On the outside of the pane. Also not a fault, quite the opposite: it means your glass insulates so well that hardly any heat escapes. The outer pane then cools below the dew point. You see this mostly with HR++ and triple glazing on clear mornings.
- Between the panes. This is a fault. The sealed unit has failed.
Why a failed unit cannot be repaired
A sealed unit is a closed system. Between the panes sits a spacer bar containing a desiccant (silica gel), and the cavity is filled with argon, closed off by a double seal. As soon as that seal breaks somewhere. Through ageing, movement of the frame or a production fault, two things happen: the argon escapes and moist air gets in. The desiccant absorbs that moisture at first, but at some point it becomes saturated. From then on the moisture condenses on the glass.
You will find methods online where a hole is drilled in the glass to “blow the unit dry”. That removes the visible moisture temporarily, but the unit stays open: the argon is gone, the insulation value is lost and the moisture comes back. It is not a repair, it is a postponement.
What does work
Replacing the unit. If the frame is otherwise still sound, the glass alone can be taken out. That is the cheapest solution and often sorted within a day.
Replacing frame and glass. If the frame is at the end of its life too. Rotten, sticking, draughty. It is a waste to put new glass in an old frame. On top of that: only by replacing frame and glass together do you qualify for the higher ISDE rate (€ 111 per m² for triple instead of € 25).
Is it still under warranty?
Insulating glass usually carries a 10-year warranty against internal condensation. Do you know when the glass was fitted, and by whom? Check that first. A production year is often stamped on the spacer bar, that gives an indication of its age.
Can you prevent it?
Partly. A failed unit is usually down to age, but these things help:
- Make sure the frame drains properly; water standing on the bottom sill attacks the seal.
- Do not stick film on the pane and do not let blinds sit tight against it, trapped heat puts strain on the edge seal.
- Keep the ventilation openings in the bottom sill clear; they are there for a reason.
Curious what it would come to for you?
Request a no-obligation quote or book a free measuring visit. Our own surveyor comes round, takes the measurements and advises you on the spot, you are under no obligation.