Double glazing repairs and maintenance

Double glazing should last for many years and weather well – that’s what it is designed to do. But 13% of the double glazing owners we spoke to had problems in the first 10 years after installation. Plus, as double glazing gets old, it may need repairs and eventual replacement.

If you end up needing to replace your double-glazed windows or doors, see the best double glazing brands according to their customers.

How do I know if my double glazing needs replacing?

Signs that your double-glazed windows or doors may need replacing include:

• Draughts
• Leaks, letting water in
• They allow excessive amounts of noise in
• The uPVC is yellowing, or timber is cracking
• There is visible damage, particularly to the seals
• They are difficult to open, close and lock, or are sticking
• They’re often covered in condensation, particularly between the panes of glass.

If they're not too extensive, some of these problems can be repaired. It’s worth speaking to a double glazing expert to establish what can and can't be fixed. Bear in mind that installers may not be willing to fix problems with double glazing they didn’t install.

Most common double glazing faults

The most common problem that double glazing owners in our survey reported post-installation was the windows or doors becoming difficult to open or close. Three in 10 of those who had a problem experienced this. All had bought their double glazing in the past 10 years.

This was followed by windows or doors dropping or sagging over time so they don’t fit as well.

• 34% – Windows or doors becoming difficult to open or close
• 18% – Windows or doors dropping over time so that they don't fit as well
• 15% – Locks not working
• 12% – Seals around doors or windows failing
• 9% – Glass steaming up or problems with condensation
• 5% – Double glazing cracking or shattering

More reassuringly, 77% of people said they had no issues with their double glazing, including with buying it and having it installed, in the first 10 years.

Can I fix double glazing that’s difficult to open or has sagged?

Difficulties with opening and closing your doors and windows may be owing to:

• The mechanism being stiff (if they’re doors or casement windows with hinges)
• The lock/handle catching or being faulty
• The hinges having moved or become loose

In the first instance, try oiling the mechanism, hinges, handles, or places where the windows or doors pass the frame (for example, if they’re sash windows) to see if that helps.

You can also try adjusting screws to tighten hinges or mechanisms. If you think these need replacing instead, contact the company you bought the window or door from.

Difficult-to-open double glazing or that which has dropped or sagged can also be caused by the weather. Extreme temperatures can cause the frame to expand or shrink and therefore the window or door won't move as smoothly – it might ‘stick’.

Wiping the frames with cold water can sometimes help shrink them down slightly – but you shouldn't have to do this regularly.

If the problems aren’t severe, try waiting until cooler or warmer weather to see if it resolves itself. But if either problem is persistent or has a significant impact (for example, preventing you from being able to shut or lock your door), contact the company you bought it from.

Check our guide to your rights with double glazing. 

How do I get rid of condensation or demist my double glazing?

Condensation or ‘steamed-up’ glass can occur if there isn’t enough ventilation in a house or room. Even newly installed double glazing can experience issues if this is the case. It can even cause it in some instances – homes need to breathe, and energy-saving measures can cause all moisture to be trapped inside.

This can be a particular problem in winter, when it’s cold outside and warm in your home. The moisture collects on cold surfaces, such as glass.

To reduce it, make sure you let fresh air into rooms as much as possible. You can also consider installing ventilation - for example air bricks, extractors or vents in window and door frames.

Trickle vents can often be added to existing double-glazed windows to allow some fresh air in without allowing the heat in your home to escape. You can open and close them as you wish.

If you're choosing new windows, consider installing one or two smaller ones, rather than all large ones – which you won’t want to have open all of the time.

You could also consider tilt-and-turn windows and doors: these let you tilt the window or door to let in a small amount of air while keeping them locked. Some windows also have the option to lock them slightly open. Find out more in our guide to choosing double glazing.

If vents aren’t an option for you, consider investing in a dehumidifier and check our full guide to getting rid of condensation.

If the condensation is between the glass panes, this suggests that the seals are broken or no longer working properly. This shouldn't happen with new double glazing.

Some companies offer to drill misted-up double glazing to draw out the moisture inside. It costs around £45 plus VAT.  However, if successful, this is likely to be a short-term fix. A plug is inserted into the gap that was drilled, but it often comes loose again in six months.

Keep reading to find out about repairing broken seals.

Do I need to replace broken seals on double glazing?

You can leave broken window or door seals, unless they are causing problems with condensation, draughts or allowing leaks to occur.

Reasons seals can fail include:

• The elements – for example wood rotting, warping or expanding in very damp conditions
• Condensation build-up on the window – over time, mould can form and damage the seals
• Using a pressure washer to clean your windows – this can weaken their seals

However, if your window seals have failed in the first couple of years after manufacture, this may be due to mistakes in their manufacture or installation. For example, the sealant material may have been tainted, had insufficient time to cure or the installer may have accidentally punctured it.

Window seals can sometimes be replaced without the entire window or door being replaced. This is easier to do on frames where the seals (also called gaskets) are separate, rather than built-in.

Where the seal can't be changed on its own, sometimes the glass can be replaced instead of the whole frame. The benefit of this, compared with just replacing the seals, is that the gas between the panes (which stops heat passing through) will also be restored.

Otherwise, the entire window can be replaced. Either way, contact the company you bought the double glazing from as soon as possible.

How do I fix a double glazing window handle or lock?

If the problem lies with heat or the mechanism getting stiff, try the tips above for cooling it down or oiling it.

If the lock is completely broken, you may be unable to open the window, or unable to lock it. In both cases, you’ll need to replace the lock.

Usually this can be done without having to change the entire frame.

You could try to replace it yourself, depending on the type of lock. However, this might affect the seals and is likely to void your warranty.

Locks shouldn't fail after only a short time, so we’d recommend calling the company if your window or door is within warranty.

If you need to call a locksmith, rather than the company, then this could also void your warranty. However if it was an emergency situation – perhaps you couldn’t lock your door securely at the weekend when the company was shut – you might be able to argue for a faulty goods claim and compensation for the cost of the locksmith.

Know your rights to refund, repair or replacement.

Can I replace double glazing myself?

New double glazing must meet certain building regulations. It must be approved by either the local council's building control department or an installer registered with a Competent Person’s Scheme who can verify the work themselves.

It’s therefore not advisable that you install your double glazing yourself.

We’d always recommend using someone signed up to a Competent Person’s Scheme, so that you don’t have to get building control involved. All Which? Trusted Traders have been through our rigorous checks to ensure that they have the right qualifications and insurance to carry out work they’re employed to do. 

We've made it simpler and easier for you to find reliable tradesman in your area. You can use our Trusted Trader search tool below to find reliable glaziers in your area.

How to get your double glazing fixed

Under the Consumer Rights Act 2015, you're entitled to have double glazing that is:

• Of satisfactory quality
• Fit for purpose
• As described
• Fitted with reasonable care and skill.

The company you bought it from should rectify any problems that occur to indicate the windows or doors are faulty.

Double glazing comes with a warranty, often of 10 or 20 years, but some companies give a lifetime guarantee. Check what yours covers and until when. For example, some only include hardware fixed in the first five years after installation. Read the next section to find out more.

If you have a problem, the first step is to contact the company you bought from.

We recommend that you contact the provider as soon as you notice the issue, in phone or in person, and follow this up in writing. Ideally this should be an email or letter, rather than text message.

Having everything in written form, including images where relevant, will make it easier if the company isn’t helpful or the problem continues.

Ask the company for written confirmation that you've notified it of the problem, plus any agreements to fix it, including dates.

Some 62% of those who had a problem with their double glazing (including buying, installation and problems since) complained to the company. Of those, 57% said their complaint was resolved.

Is my double glazing covered by a guarantee?

Double glazing comes with a warranty - typically of 10 or 20 years, although some are lifetime guarantees.

Check the details of your warranty to see if your issue is covered. If you've bought a property with double glazing you should have received details of the installation from building control, plus information about its warranty.

Read more about whether you can use a manufacturer’s warranty.

But even if the issue occurs after the warranty has run out, you're still protected by the Consumer Rights Act. You will have to prove that the fault occurred because of a defect with the product or installation (as opposed to wear and tear or something you have done). Sometimes it can be worth calling in an independent expert, such as a surveyor, to prove this.

First, read our handy guide on how to complain if you’re unhappy with a trader’s work.

Our double glazing research

We surveyed 3,409 people in August 2022 about their experiences with the company from which they had bought, and that had installed, their double glazing in the past 10 years.