Checking for Gaps Around the Window Frame
Checking for gaps around the window frame is one of the most effective ways to stop draughts in double-glazed windows. Even high-quality sealed units will let heat out if there's a gap where the frame meets the wall or where the sash closes. Small gaps can create a wind-tunnel effect that draws in cold air and pushes warm indoor air out, which can raise your energy bills and encourage condensation.
You should hold the back of your hand or a strip of tissue along the frame's perimeter, hinges, and sashes; any movement or a noticeable chill is a sign that there's a gap. You should also check for visible cracks in the frame's caulk/silicone, loose trims, flattened rubber gaskets, misaligned hinges and light around the sash corners.
Inspecting the Window Seals and Gaskets
Even if the double-glazing is strong, air can still seep in if the sash isn't firmly compressed against its seals, or when the glazing and gaskets have hardened, shrunk, or become loose.
Different seals can fail in different ways. Bubble/flipper weather-strips on the sash can lose resilience and stop sealing under multipoint locks. Wedge or glazing gaskets that hold the glass can shrink, which can create hairline paths for air and water between the bead and the glass. The frame perimeter sealant may crack, causing cold air to seep in, even when the gasket is fine.
However, fixing this issue is relatively straightforward. You can replace the weather-strips like-for-like, buy EPDM or Q-Lon equivalents, and push them in so the joint finishes at the hinge side, not at a corner. For double-glazed gaskets, you can remove the beads, swap the gasket, and refit it with the correct packers to keep the sash stable.
It's also important to restore the compression. You can do this by adjusting the friction-stay hinges and strike/keeps so that the sash closes evenly against the seals. You can then reseal any cracked frame-to-wall joints with low-modulus neutral-cure silicone.
How to Reseal or Replace Worn Seals
Resealing or replacing worn seals is a practical way to fix draughts in double-glazed windows. On a windy day, run the back of your hand or a tissue strip against the frame to see any movement, then close the window on a strip of paper; if it pulls out easily, there's poor compression.
To replace the perished sash weather-strips, you should identify whether the gasket is a bubble, flipper, fin, or compression model. Then, take a 50-100 mm sample or measure the groove and buy a like-for-like EPDM or Q-Lon seal. Then, pull out the old strip, clean the groove with mild soapy water and let it dry. Push-fit the new seal without stretching it and place the joint on the hinge side, not the corner. Then, lightly spray the seal with a silicone spray to harden it and keep it in place.
When to Consider Professional Repair or Replacement
If you’ve replaced the weather-strips, adjusted the locks, and resealed the frame-to-wall joints and still feel cold air seeping through, you may have warped sashes, distorted frames or a poor original installation. These issues cannot be fixed with a quick DIY; instead, they need to be professionally refitted.
Condensation inside the glazing cavity means that the sealed unit has failed, and no amount of ventilation or wiping will clear it away. The usual remedy for this issue is to replace the sealed unit, ideally with low-e, argon-filled glass and warm-edge spacers to improve your indoor comfort and efficiency.
Rotten timber, cracked uPVC welds, broken aluminium thermal breaks, or visible daylight around the sash are signs that the window's structure is damaged. In this case, a full repair or replacement may be the safest option. Additionally, any leaks around the beads or sills, stained reveals, or recurring mould are signs of damaged gaskets or failing glass racks. A trained specialist can re-pack the unit, replace the gaskets and correct the panel's alignment.
We provide fast, reliable double-glazing repair services to restore clarity, warmth and security to your property. We can fix misted units, damaged seals, panes and more.
