Small draughts often come from small parts. On UPVC windows, the gasket is the soft rubber seal that keeps out cold air, rain and noise. When it flattens or splits, you feel it. This guide explains what to check, simple fixes, and when a tidy replacement is the smartest move.
WHAT A UPVC WINDOW GASKET DOES (AND WHY IT MATTERS)
The gasket sits between the sash and the frame. When the window closes, it compresses to form an airtight, watertight seal. That seal blocks sneaky draughts, cuts outside noise, and helps your heating work less hard. Common profiles are bubble (rounded), flipper (a thin flexible fin) and wedge (a firm strip that locks the glass in place).
Good gaskets feel springy and make light, even contact all round. Early warning signs include flattening, shiny wear marks, gaps at corners, whistles on windy days, and light coming through where it should not. If you notice these, a quick check and tidy-up can make a big difference to comfort and energy use.
HOW WORN GASKETS CAUSE COLD SPOTS AND HEAT LOSS
Rubber compresses thousands of times over its life. Sunlight, cleaning chemicals and age also harden it. As it flattens or shrinks, tiny gaps appear. Corners, the hinge side and latch points often go first because they take the most stress. On a cold day, those gaps let chilly air snake in behind your curtains and along window boards.
Little leaks create cold spots and small convection currents that make a room feel drafty and uneven. You might see curtains move slightly or feel a cool flow at ankle height. That discomfort nudges the thermostat up, so you burn more energy. If this sounds familiar, see our guide on why cold air gets through double glazing.
QUICK CHECKS YOU CAN DO IN 5 MINUTES
Do the paper test. Open the window, place a strip of paper across the gasket, then close and lock the sash. Gently pull. You should feel firm resistance all the way round. If it slides out easily in places, compression is weak there. Repeat on each side, especially at corners and the hinge edge.
At dusk, shine a torch from outside while someone looks for light leaks inside. On a breezy day, use the back of your hand to feel for cold air and listen for rattles or whistling. If you try incense or a smoke pencil, keep flames away from frames, curtains and children. For more tips, see how to fix a draught on a UPVC window.
This image was generated with AI and may not always represent the product or service exactly.
WHAT FAILING GASKETS LOOK AND FEEL LIKE
Look for flat, shiny lines where the rubber has been pressed hard for years. Check corner joins for splits, gaps or shrinkage. Press the seal gently; if it feels hard, brittle or stays squashed, it is past its best. Also look for sections dropping out of their groove or seals that pull free too easily.
Condensation around the perimeter can be a clue. A poor seal chills the glass edge, so water collects there and mould can follow. Clean light mould with mild detergent and a soft cloth, then dry thoroughly. If in doubt, compare your symptoms with our guide to common window seal failures.
SIMPLE FIXES BEFORE YOU REPLACE THE GASKET
Start with a clean. Use a soft brush and a damp cloth to remove dirt, paint flakes and old silicone from the gasket and its groove. Clean contact faces on the sash and frame too. You’ll often get a better seal straight away. Avoid harsh solvents that can dry rubber.
If compression is uneven, small hinge or lock keep adjustments can help. This improves how the sash pulls onto the seal. If you are unsure, get help: a neat tweak goes a long way. See our pages on the window hinge and the window lock for what we adjust. To care for rubber, use a silicone-safe conditioner. Do not use petroleum products; they can swell or damage seals.
WHEN GASKET REPLACEMENT IS THE RIGHT MOVE
Replace when seals are badly flattened, split, shrunken, missing, or won’t stay in the groove. Matching the exact profile and size matters. Bubble, flipper and wedge gaskets compress differently and sit in different grooves. A near match may look fine but still leak.
Fitting involves cutting cleanly, joining corners neatly and seating the seal evenly all round. It’s easy to waste time and material if the profile is wrong or corners are messy. A professional fit gives a tidy finish and a longer-lasting seal, often for far less than new windows. Learn more about our gasket seal repairs and replacements.
WHEN IT’S NOT (JUST) THE GASKET: OTHER ISSUES TO CHECK
Misted or foggy glass is a different failure. It usually means the double-glazed unit’s edge seal has blown, letting moisture get between the panes. Replacing the unit fixes the view and the insulation; new gaskets alone will not clear the fog. A draught plus misting may mean you need both a unit and gasket check.
Loose hinges, worn locks or a misaligned sash reduce compression and can mimic a failed gasket. Frames can also move slightly over time, leaving uneven gaps. If symptoms are mixed, get a proper assessment. Fixing the root cause once is cheaper than chasing recurring draughts all winter.
This image was generated with AI and may not always represent the product or service exactly.
COSTS, SAVINGS AND WHAT TO EXPECT DURING A REPAIR VISIT
Price depends on window size, the gasket profile, the number of openings and any hinge/lock adjustments needed. On a typical visit, we assess the windows, match the profile, replace tired sections, adjust compression, then test for draughts and smooth operation. We keep work tidy and disruption low.
Afterwards, you should notice warmer rooms, fewer cold spots and less outside noise. With the leaks sealed, your heating runs more efficiently too. For a clear breakdown of how we work and what we fix, see Plastic Doctor’s window repairs.
LANDLORDS: STOP HEAT LOSS AND CALL-OUTS IN RENTAL HOMES
Small gasket faults add up to bigger winter complaints. Quick checks between tenancies keep homes comfortable and bills sensible. Add the paper test and a visual seal check to routine inspections, and you’ll catch most issues before they become call-outs.
We can refresh seals, adjust compression and sort minor hardware wear in one visit. That helps with EPC performance and reduces cold-weather emergencies. Clear, fast communication keeps tenants happy and your schedule on track.
NEED HELP FAST? LOCAL GASKET AND DRAUGHT REPAIRS
If your windows feel draughty, don’t wait for the next cold snap. Plastic Doctor offers prompt, affordable gasket replacement and UPVC maintenance across Essex and Suffolk. We turn up on time, work cleanly and explain what we’re doing.
Book a quick inspection. In many cases, a simple gasket replacement or a small hinge/lock adjustment solves the problem the same week. You’ll feel the difference the moment the heating comes on.
FAQs
How Do I Know Which Gasket Profile I Need?
Remove a small, loose section and compare it to a new sample. Match the shape (bubble, flipper, wedge) and the base size. If in doubt, we identify the profile for you on site.
Can I Replace Just One Window’s Gaskets?
Yes. You can replace seals on a single sash or a few problem windows. We only recommend whole-house replacement if many windows show the same failure.
Will New Gaskets Stop Condensation?
They reduce perimeter condensation by removing cold spots at the edge. They will not clear mist between panes; that needs the glass unit replaced.
How Long Do UPVC Gaskets Last?
Typically 10–20 years, depending on sunlight, use and cleaning products. Signs like flattening, splits and brittleness mean it’s time to replace.
Is Lubricant Safe On Rubber Seals?
Use a silicone-safe rubber care product sparingly. Avoid petroleum-based sprays and solvents, which can swell or damage the seal.
What’s The Difference Between Bubble And Wedge Gaskets?
Bubble gaskets compress between sash and frame to seal. Wedge gaskets lock the glass into the frame and support it; they do a different job and are not interchangeable.
