If your double glazed window is misty, draughty or hard to close, you may be able to keep the frame. A repair starts with finding the faulty part. A sound frame can often take a new sealed unit, handle or hinge, while a draught may need a seal or alignment repair. The checks below will help you describe the problem when the window or door is surveyed.
Diagnose the fault before ordering parts
Start with where the moisture is. Wipe both accessible faces of the glass. Moisture on the room side points to condensation inside the house. Moisture on the outside can occur on well-insulated glazing. Fog, droplets or staining between the two panes mean the sealed unit has failed, and you cannot wipe that away. In most cases the sealed unit can be replaced without replacing the whole window.
Try the handle gently and note where the sash catches or where the draught comes through. Air around the opening edge points to a different repair from air at the joint between the frame and the wall. Leave cracked glass or an unsafe sash alone and arrange an inspection. A door that will not lock also needs attention.
| Symptom | Likely starting point | Usual repair route |
|---|---|---|
| Mist trapped between the panes | Failed sealed glass unit | Replace the sealed unit in a sound frame |
| Handle spins or will not turn | Handle spindle or locking mechanism | Identify the faulty part before replacement |
| Sash rubs or will not pull tight | Hinges, alignment or keeps | Adjust or replace the hardware |
| Draught at the opening edge | Gasket, alignment or locking pressure | Inspect the seal and sash fit |
| Patio door sticks on its track | Rollers, track or door alignment | Inspect the running gear and track |
Seven fixes to check before replacing the frame
1. Replace a misted sealed glass unit
A double glazed unit has two panes sealed around the edge. When that edge seal fails, moisture gets into the cavity and causes persistent misting, often called blown double glazing. The lasting fix is a new sealed unit. Drilling the glass or sealing the outside of the frame will not restore the edge seal. The new unit is measured to size, and the glazing beads, packing and drainage are checked when it is fitted.
You can keep the frame if the sash fits properly and can support the new unit. Resealing an external joint can stop air or water getting in around a frame, but it cannot restore the seal inside a failed glass unit.
2. Replace cracked or broken glass safely
Have cracked glass assessed even if only one pane looks damaged. The unit can then be measured and specified with glass suited to its position, including safety glass where it is required. Leave loose shards and glazing beads alone.
With a sound sash and frame, a cracked pane is usually solved with a new sealed unit. If the same impact has damaged the frame, it needs a wider assessment.
3. Fix a stiff, loose or broken window handle
A handle can work loose at its fixings or wear at the spindle. Sometimes the stiffness comes from a seized lock or a sash that is sitting out of square. Test the handle and lock with the window open, without forcing them. A new handle is only needed when the handle itself has failed.
The replacement must match the handle type, spindle and fixing positions. A lock that does not engage is a security fault and should be looked at promptly.
4. Adjust or replace worn hinges
A casement that drops, rubs or leaves a gap at one corner may have worn friction hinges or loose hinge fixings. The replacement hinges need to match the window, and the sash alignment should be checked once they are fitted. Forcing the window shut can damage the lock and the frame.
Where the sash or frame is distorted, new hinges may lose their adjustment again.
5. Renew failed weather seals and deal with draughts
A sash gasket can flatten, pull away or tear and let in cold air. The replacement seal needs the correct profile. An extra adhesive strip can stop the window closing properly or the lock engaging. Worn hinges, poor locking pressure and gaps between the frame and the wall can also cause draughts.
If water pools on the frame, include drainage in the inspection. You can clear an accessible drain slot, but a leak that keeps coming back needs its source traced. More silicone may only hide the problem. Replacing worn seals alongside other repairs can keep a serviceable frame in use for longer.
6. Repair door locks, keeps and alignment
If you have to push or lift the door itself before it will lock, the hinges may have dropped or the keeps may be out of line. The handle, cylinder and multipoint mechanism are separate parts. Once the fault is identified, an adjustment or a replacement part may restore closing and security without a new door.
Do not keep forcing the key or handle. If the door cannot be secured, you will need urgent help elsewhere, as Cii does not offer same-day or emergency callouts. The same diagnosis applies to uPVC doors, composite doors and French doors, although their hardware is not interchangeable.
7. Service sliding patio door running gear
A sliding door that drags may have worn rollers, a dirty or damaged track, or a sash out of alignment. The inspection needs to separate running-gear faults from problems with the glass or the lock, so the rollers, track, seals and lock engagement are all checked on the same visit.
Large glazed door leaves are heavy, so leave removal to a fitter. If the door is old enough that matching rollers or locks are hard to source, the survey should set out the alternatives rather than promise an adjustment. One of those may be a new aluminium sliding patio door sized to the opening.
Repair, refurbish or replace the whole window?
Start with the frame. A square, secure window with one failed part is usually a repair candidate. If the hardware, gaskets and glass have all worn together, ask for a combined repair quote that covers each fault. Piecemeal work makes less sense when the frame is warped, cracked or insecure.
| Condition | Sensible next step | Why |
|---|---|---|
| Sound frame, one misted unit | Replace the sealed unit | The existing frame stays in place |
| Sound frame, recurring draughts and stiff operation | Survey the hinges, seals, locks and alignment | Faults that affect each other are fixed together |
| Sound frame, older glass but working hardware | Ask about upgrading the sealed units | A correctly specified new unit may improve performance without a new frame |
| Warped or damaged frame, repeated faults across the opening | Compare full replacement with the repair quote | New parts may not sit or seal properly |
To upgrade the glass, the existing sash must take the new unit's thickness, weight and specification. That applies to bay and tilt and turn windows as well as casements, and an aluminium window needs a unit matched to its glazing system. If the sash cannot take it, or the frame is failing, a full replacement may make more sense. Ask the surveyor what will stay and whether a new energy-efficient unit can improve thermal performance. If you want a different style altogether, compare replacement window options with glass-only work. Our guide to uPVC vs aluminium window quotes explains how to compare complete windows like for like.
What affects the cost of a repair?
A handle change and a made-to-measure sealed unit are very different jobs. Unit size and glass specification, access, matching hardware, the number of openings and the condition of the frame all affect parts and labour. A door may need work on several locking points, and a sliding patio door can need running gear made for that model.
The quote should list diagnosis, parts, labour and any glass or frame replacement as separate items. Point out every affected opening at the survey so you can weigh individual repairs against a wider job. A quote to "reseal" a misted unit does not cover the same work as supplying and fitting a new sealed unit. Ask for an itemised written quote after survey.
How Cii handles window and door repairs
Cii Double Glazing is a family-run business, established in 2009, with over 55 years of combined experience in the team. We repair windows and doors of all brands across Essex, Hertfordshire and East London, including ones we did not fit. Every repair starts with a survey to diagnose the fault. We then order any parts needed and book a separate repair visit. We do not offer same-day or emergency repairs.
When you get in touch, tell us which openings are affected, where you see condensation and whether the door locks. If the frame is sound, we will recommend the repair. If it is not, we will explain the replacement options, which our own team surveys and fits with a 10-year installation guarantee. Book a free home survey and written quote to find out which applies to yours.
FAQ
How much does it cost to fix a double glazed window?
It depends on whether the fault is a handle, hinge, gasket, lock or sealed glass unit. Size, glass specification, access and the number of openings also affect the price. Ask for an itemised written quote after survey, which separates the cost of a targeted repair from a full replacement.
Is blown double glazing covered by insurance?
Cover depends on the cause and the wording of your policy. Gradual seal failure and accidental damage are treated as different events. Check your policy and any existing glazing guarantee before arranging work, and describe the cause of the damage accurately.
What does failed double glazing look like?
A failed sealed unit usually shows fog, droplets or staining trapped between the two panes, where you cannot wipe it away. Moisture on a glass surface you can reach has a different cause and does not by itself mean the unit has failed.
What are the common problems with double glazed windows?
Common faults include misted sealed units, cracked glass, stiff handles, worn hinges, loose gaskets and locks that no longer engage properly. The fix depends on whether the fault is in the glass, the opening hardware, the seals or the frame.
Can a window or door be repaired if another company installed it?
Yes, in most cases. Cii repairs windows and doors of all brands, as long as compatible parts are still available. The survey confirms the parts needed before the repair visit is booked.
