Home › Doors & Windows › uPVC Window Not Sealing

DRAUGHTS & SEALS

uPVC Window Not Sealing

A uPVC window that does not seal usually has poor compression from worn gaskets, dropped hinges or misaligned locking hardware.

≈
!

Do not block required ventilation or drainage

Some gaps, vents and drainage slots are intentional. Fire doors, external doors and emergency windows may also have specific sealing requirements.

MOST LIKELY CAUSES

Start with the exact air or water path

Flattened gasket The seal no longer springs back against the sash.
Dropped sash The hinge side has moved out of alignment.
Misadjusted cams or keeps The sash is not pulled tightly into the frame.
Distorted frame or sash The opening is no longer even.
◫ Symptom variations Match the draught, gap or seal pattern. ⌄
  • Draught at one side
  • Noise from outside increases
  • Handle locks but sash feels loose
  • Seal gap visible at corner
  • Water marks near gasket
✓ Quick checks Safe checks before replacing seals. ⌄
  1. Inspect the gasket around the full perimeter.
  2. Check whether pulling the sash tighter stops airflow.
  3. Compare gaps on hinge and handle sides.
  4. Inspect locking cams and keeps.
  5. Check for visible frame bowing.
Important: Find the exact leak path first. Replacing the wrong seal can make closing harder without fixing the fault.
1 Step 1 — Check alignment before replacing seals Make the smallest safe correction and retest. ⌄

Correct a dropped sash first.

2 Step 2 — Adjust compression carefully Make the smallest safe correction and retest. ⌄

Use manufacturer-suitable cam or keep adjustment.

3 Step 3 — Replace the gasket if worn Make the smallest safe correction and retest. ⌄

Match the profile and fit without stretching.

⌁ Why the problem happens How compression, alignment and weathering affect sealing. ⌄

uPVC seals depend on several locking points applying even pressure. Too little pressure leaks; too much can damage handles and gearboxes.

⌘ Advanced checks Further diagnosis for persistent sealing faults. ⌄
  1. Identify mushroom-cam adjustment.
  2. Check hinge stack and wear.
  3. Measure gasket profile.
  4. Inspect frame fixing points.
  5. Check drainage routes.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Allen keys
  • Screwdrivers
  • Tape measure
  • Plastic trim tool
  • Replacement gasket
▣ Parts or improvements that may help Common sealing products linked to this problem. ⌄
  • Window gasket
  • Keeps
  • Espagnolette
  • Friction hinges
  • Handle
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • The frame is badly distorted.
  • The lock is stiff or failing.
  • The sash is large or high-level.
  • Water is entering around the frame.
  • The window cannot be secured.
? Frequently asked questions Common draught and seal questions. ⌄

Can I adjust the locking cams?

Many can be adjusted slightly, but over-compression can damage the mechanism.

Should I replace the gasket first?

Only after checking alignment and compression.

Why has the seal failed at one corner?

The sash may have dropped or the gasket may have shrunk.