The short version
- Double glazing complaints have no single ombudsman: each dispute scheme covers only its own members.
- Write to the installer first and allow 14 days for a reply, as DGCOS asks.
- FENSA and CERTASS handle Building Regulations faults only, not refunds or compensation.
- Disputed court claims of £10,000 or less go to free court mediation first.
How do I complain about a double glazing company?
Complain to the double glazing company in writing first, then work up five steps until the complaint is settled:
- Write to the installer and allow 14 days for a reply.
- Use the installer's dispute resolution scheme, if it belongs to one.
- Report a Building Regulations fault to FENSA or CERTASS.
- Call the Citizens Advice consumer service, which passes cases to Trading Standards.
- Make a court claim as the last step.
Keep every letter, email and photo from the first step. Each body further up the ladder asks what the installer was told and when.
Is there an ombudsman for double glazing?
No, there is no single ombudsman for double glazing, and each scheme covers only the customers of its own members. Despite its name, the Double Glazing & Conservatory Ombudsman Scheme (DGCOS) is a private company limited by guarantee that runs a dispute resolution scheme approved by the Chartered Trading Standards Institute (CTSI).
DGCOS gives customers of its members free mediation and, once its own process is complete, free access to an independent ombudsman. The ombudsman's decision "is binding on the member but not on you", and it covers installations made while the firm was a member, even if the membership has since lapsed.
| Scheme | Who it covers | What it does | Cost to you |
|---|---|---|---|
| DGCOS | Customers of DGCOS members, for homes in England, Scotland, Wales or the Isle of Wight | Mediation, then the Dispute Resolution Ombudsman | Free |
| Glass and Glazing Federation (GGF) Complaints Service | Domestic customers of full GGF members, not affiliate members | Contacts the member on your behalf | Free |
| Home Improvement Consumer Protection Scheme (HICS) | Customers of HICS members | Mediation | Free |
Ask the installer which scheme it belongs to, ideally before you sign. The Digital Markets, Competition and Consumers Act 2024 includes a duty on traders to notify consumers of their dispute resolution arrangements.
Step 1: put the complaint in writing to the installer
Write to the installer that sold you the windows, even if a subcontractor fitted them, and give it 14 days to reply. Citizens Advice says to take the problem up "with whoever arranged the installation", and DGCOS asks you to allow 14 days before it steps in. Your letter covers four points:
- what the problem is, fault by fault
- how you want it resolved
- dated photos and the dates you first reported it
- the date by which you expect a reply
Follow every phone call with a letter or email, and avoid text or WhatsApp, as Which? advises. Ask for the installer's complaints procedure too: CERTASS requires its members to provide a copy on request.
Our guide to badly fitted windows covers listing fitting faults and the Consumer Rights Act wording to use.
Step 2: use the installer's dispute resolution scheme
Use the installer's dispute resolution scheme once the installer has had its chance to answer, because DGCOS, the GGF and CERTASS all refuse a complaint the installer has not had the chance to answer. DGCOS runs four stages:
- Submit the complaint by the online form, by email or by phone on 0345 053 8975.
- A mediator reviews it, contacts you and the member, and may arrange an independent inspection of the installation, free to you.
- DGCOS makes a decision on the evidence, with a written explanation.
- Escalate to the Dispute Resolution Ombudsman, free of charge, if the dispute is still not resolved.
DGCOS may refuse a complaint when the contract value is over £150,000, when a court or another scheme is already involved, or when you signed the contract outside the firm's membership.
The GGF Complaints Service is free for domestic customers of full GGF members. It accepts a complaint only after you have used the installer's own complaints process, and then phones the member on your behalf. For contract disputes, the GGF recommends Citizens Advice.
When FENSA or CERTASS can help
FENSA and CERTASS help only when the complaint is about Building Regulations compliance, not refunds, compensation or the contract. FENSA takes a complaint when four conditions are met:
- the installer is a FENSA Approved Installer and still trading
- the work was completed less than six years ago
- the work was a window or door replacement in a home in England or Wales
- the complaint concerns compliance with Building Regulations
FENSA cannot help with customer care, product quality, compensation, refunds, contractual issues or the guarantee, nor with conservatories, porches or new builds. It may help in some cases when the installer is also a TrustMark member.
CERTASS limits its complaints to Building Regulations and industry codes of practice and stays out of contractual or financial disputes. It accepts a complaint only after the installer's own procedure is exhausted, gives the installer the chance to return and put the work right, and acknowledges complaints within 10 working days.
Step 3: Citizens Advice and Trading Standards
Call the Citizens Advice consumer service to involve Trading Standards, because you cannot usually report a trader to Trading Standards yourself. The adviser can pass your case to Trading Standards, but cannot make a complaint for you or take legal action on your behalf.
- England: Citizens Advice consumer service, 0808 223 1133 (Relay UK: 18001 then 0808 223 1133)
- Wales, in Welsh: 0808 223 1144
- Scotland: Advice Direct Scotland, 0808 164 6000
Step 4: make a court claim
A court claim is the last step: you apply to a county court, online or by post, for the money the installer owes you, such as the cost of putting the work right. The court fee depends on the amount claimed, and GOV.UK lists the court fees by band.
Disputed claims of £10,000 or less go to mediation first: GOV.UK says you will be told you must attend, and the court-organised mediation is free. Scotland and Northern Ireland have their own court claim processes.
A contract claim must start within six years in England and Wales (Limitation Act 1980, section 5) and five years in Scotland (Prescription and Limitation (Scotland) Act 1973, section 6).
Use the dispute scheme before the court: DGCOS cannot investigate once you have taken legal action. Which? advises a final ultimatum first, backed by quotes from other installers for fixing the problem, which show the company how much you will claim.
If you paid by card, or the installer has stopped trading
A credit card payment gives you a second party to claim from. Under Section 75 of the Consumer Credit Act 1974, the card provider is jointly liable for a single item with a cash price over £100 and up to £30,000. Our guide to the double glazing deposit covers card payments and deposit insurance.
An installer that has stopped trading cannot answer a complaint, so the claim moves to any insurance-backed guarantee or deposit insurer. Our guide on what happens if your double glazing company goes bust sets out the order.
Need the work put right? Compare quotes from other installers
Quotes from other installers show what putting the work right involves, and Which? advises getting them before a final ultimatum. Use the same written specification for every quote so the figures compare.
Get quotes from other installers
Free quotes from local installers who cover your postcode, to refit or replace the windows.
Questions people ask
What are some common problems with double glazing?
Problems after installation are the most common kind, reported by 13% of the 3,409 double glazing owners Which? asked. Problems with the installation (8%), delivery (5%) and purchase (2%) were less common. Faults within the guarantee period go to the installer under your double glazing guarantee.
Which double glazing company is considered the best in the UK?
No single double glazing company is best for every home, so compare written quotes on the same windows, glass and guarantee. Our guide to double glazing installers lists the checks to run on each firm.
Is DGCOS a real ombudsman?
DGCOS is a private company limited by guarantee that runs a CTSI-approved dispute resolution scheme. It gives customers of its members free access to an independent ombudsman after its own process. It does not cover installers outside its membership.
Can FENSA make my installer fix my windows?
FENSA acts only on Building Regulations compliance, for work by a FENSA Approved Installer still trading, completed less than six years ago in England or Wales. Refunds, compensation, product quality and guarantee claims fall outside its remit.
How long do I have to complain about double glazing?
You have six years to bring a contract claim in England and Wales and five years in Scotland. FENSA takes Building Regulations complaints about work completed less than six years ago.
Is there a double glazing complaints letter template?
Citizens Advice gives wording to use: "The Consumer Rights Act 2015 says that goods must be correctly installed, if installing them was part of the contract. In my opinion, you did not install them correctly when you carried out this work." Add each fault, the fix you want and a reply date.
