TrustMark and the ECO4 insulation failures: what the official reports found

The National Audit Office and the Public Accounts Committee both examined how thousands of faulty wall insulation installations got through the quality system. This page summarises what they said about TrustMark and the wider system, and what it means for you now.

Summarised from published reports

Everything below is drawn from the NAO report (HC 1334, October 2025) and the Public Accounts Committee report (HC 1229, January 2026), linked at the end. We are not connected to TrustMark, Ofgem or the government.

What TrustMark is

TrustMark describes itself as the Government Endorsed Quality Scheme for work a consumer chooses to have carried out in or around their home. It is a private, not-for-profit company, not a regulator or a government body.

Under the system introduced in 2021, TrustMark oversees a single quality mark for retrofit work. Installers doing ECO4 work must be registered with TrustMark and certified to the PAS 2030:2023 standard, following the PAS 2035:2023 retrofit process. The United Kingdom Accreditation Service accredits the certification bodies that certify installers, and those certification bodies also act as TrustMark scheme providers. Ofgem administers ECO itself.

Key findings

A "clear and catastrophic failure"

The committee said faulty external and internal wall insulation under ECO4 and GBIS had left over 30,000 homes with defects: an estimated 98% of external wall insulation (about 22,000 to 23,000 homes) and 29% of internal wall insulation installed up to mid-January 2025, with 32,000 to 35,000 homes likely affected.

Late warning

TrustMark did not notify the Department of high levels of faulty external wall insulation until October 2024, more than two years after ECO4 began in April 2022, and raised similar concerns about internal wall insulation in November 2024. TrustMark told the committee it had shared audit results with the Department since 2022; the NAO reported that TrustMark only developed the analytical capability to spot non-compliance trends in the second half of 2024.

A system too complicated to work

The NAO concluded the schemes and the quality assurance system were overly complex, and that nobody it spoke to could fully explain how the system was meant to work. The Department accepted there were "serious failings at every level", and TrustMark accepted it should have realised much sooner that the design under-estimated the risk.

Checks paid for by the installer

Retrofit assessors and retrofit coordinators can be appointed and paid by the installer whose work they check. The NAO reported that coordinators may therefore be incentivised to approve non-compliant work.

Suspensions and reinstatements

TrustMark and the certification bodies suspended 38 installer businesses, representing 81% of the external wall insulation market. By November 2025, 22 had been reinstated after meeting TrustMark's six-point plan, including fixing the problems identified.

Slow repairs and disappearing installers

By mid-September 2025 fewer than 10% of affected homes had been found and fixed. The NAO reported that some company directors were closing and restarting businesses to avoid remediation; TrustMark told the committee it keeps a watchlist to stop a new business trading until its directors' earlier faulty work is fixed.

What has changed since

Since March 2025, retrofit coordinators must visit each project site in person. The committee noted there is still no requirement for them to be independent of the installer.
TrustMark runs the Find & Fix programme, offering a free audit to every household with ECO4 or GBIS external wall insulation. The government said in April 2026 that it should finish by May 2027.
From 17 June 2026 the Installation Assurance Authority raised its repair cover for ECO4 and GBIS solid wall insulation guarantees from £20,000 to £25,000, and the National Energy Foundation now covers some homes whose guarantee was cancelled, fraudulent or missing.
ECO4 has been extended to 31 December 2026 with no successor supplier obligation; GBIS closed on 31 March 2026.
The government consulted from 17 June to 10 September 2026 on reforming consumer protection for home upgrade schemes, including a public register of government-approved installers and a single advice and complaints service, with reforms aimed at around 2028.

What this means for you

If you already have ECO4 or GBIS wall insulation

External wall insulation: book TrustMark's free Find & Fix audit (0333 555 1234, option 1). How it works.
Internal wall insulation: if you have concerns, contact Ofgem's ECO contact centre on 0808 169 4447 or ECOhelp@ofgem.gov.uk.
A complaint about a registered business: complain to the business, then its TrustMark scheme provider, then the Dispute Resolution Ombudsman.

If you are having work done

Check the installer's registration yourself on the TrustMark register, rather than relying on a logo.
Ask who the retrofit coordinator is and whether they work for, or are paid by, the installer.
Ask which company provides the 25-year guarantee and read what it covers.
For solid walls, consider an independent survey of the property's suitability before work starts.

How to check a specialist before you agree to work

Affected by faulty insulation?

See which free audit, guarantee or complaint route applies to your home first.

See the redress routes Ask for a specialist

Sources

Last reviewed September 2026.