Double glazing repairs and maintenance

Double glazing should last for many years and weather well – that’s what it is designed to do. However, many double glazing owners have 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.

Most common double glazing faults

The most common problem faced by double glazing owners is windows or doors becoming difficult to open or close.

Other common problems include:

• Windows or doors dropping over time so that they don't fit as well
• Locks not working
• Seals around doors or windows failing
• Glass steaming up or problems with condensation
• Double glazing cracking or shattering

We've listed some DIY advice for tackling common double glazing problems in this guide. 

Does your double glazing need 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, so you may not need to leap straight to a replacement. Speak to a double glazing expert to establish what can and can't be fixed. Start with the person who fitted it in the first place, if you still have their details. If not, you'll need to find a third party expert willing to take on repairs.

DIY tips: How to 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 dropping/sagging can also be caused by extreme weather. Very hot or cold 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.

You may need to wait until cooler/warmer weather to see if the problem resolves itself. But if it 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 companies 

DIY tips: How to get rid of condensation or demist double glazing

Condensation or ‘steamed-up’ glass can occur if there isn’t enough ventilation in a house or room. 

Newly installed double glazing can even cause the problem in some instances – homes need to breathe, and well-intentioned measures to seal up cracks and draughts can cause all the moisture your home generates (through cooking, bathing, drying clothes, and even breathing!) to be trapped inside.

This can be a particular problem in winter, when it’s cold outside and warm in your home. Moisture collects on cold surfaces, including glass windows.

To reduce condensation:

• Let fresh air into rooms as much as possible, and regularly open windows. Through winter, opening all your home's windows for a short burst of fresh air before closing them again to keep heat in. 
• You can also consider installing purposeful ventilation - for example air bricks, extractor fans or vents in window and door frames.
• Trickle vents can often be added to existing double-glazed windows to allow fresh air in without allowing the heat in your home to escape. You can open and close them as you wish.
• Take particular care to ventilate or dehumidify your home when doing things that release moisture into the air, such as cooking, showering and drying laundry.

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.

Replacing broken seals on double glazing

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

Reasons seals can fail include:

• Weather conditions – for example wood rotting, warping or expanding in very damp conditions or extreme temperatures
• 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

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 may need to be replaced. 

These are jobs for a professional installer. In the first instance, contact the company you bought the double glazing from. If you can't, you'll need to ask another installer or a repair company.

How to fix a double glazing window handle or lock

If the problem is that the lock mechanism is stiff, you may find you can solve it by oiling the lock. If the lock is jammed in extreme heat, try to cool it down.

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 you replace double glazing as a DIY job?

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.

Your rights when you have problems with your double glazing

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.

If you have a problem with your double glazing, 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.

Is double glazing covered by a guarantee?

Double glazing installations should come 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.

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.

Read more from the Which? consumer rights team on: how to complain if you’re unhappy with a trader’s work

Is it worth replacing 20 year old double glazing?

Double glazing doesn't have an infinite lifetime. Once it's twenty years old, it can become worn and less efficient. If your double glazing is very old, and you aren't happy with your home's energy efficiency, it may be time to look at replacing it. 

As years pass, the sealant between the panes of glass deteriorates, allowing moisture to enter. This can cause condensation and fogging, damaging the performance of the window. 

The quality of double glazing can determine how fast it will deteriorate, as will the weather conditions it has experienced.

Your double glazing may need replacing if:

• You can see damage to the glass
• There is fogging or condensation between the panes
• You can feel draughts or cold spots near the window

Replacing double glazing is an expensive job. Thankfully, newer, more energy efficient window panes will help regulate the temperature and comfort of your home, as well as saving money on your energy bills.