Routine audits carried out by TrustMark in October 2024 identified significant levels of poor-quality solid wall insulation installed under the Energy Company Obligation 4 (ECO4) and the Great British Insulation Scheme (GBIS), according to a written statement to the House of Commons1. TrustMark, described in the statement as the independent body that oversees the quality of retrofit work done by tradespeople working in homes, began suspending installers, and the Department commissioned a much fuller audit1.
The schemes place obligations on large and medium-sized energy suppliers to install energy efficiency improvements to homes, typically delivered through contractors. ECO4 commenced in 2022 and GBIS in 2023, and around 65,000 households have received solid wall insulation under them1. A statement made in the House of Commons on 23 January 2025 and repeated in the Lords on 29 January put the number of suspended businesses at 39, and said suspended installers would not be able to deliver new solid wall insulation under any government scheme until they had fulfilled their obligations to put issues right2. The October 2025 statement gives the figure as 38 installers suspended, with a rigorous process for reinstatement following remediation of all issues in identified properties1. The two figures differ.
The independent audit programme, launched in the spring and published on gov.uk, found that 92% of external wall insulation installations and 27% of internal wall insulation installations audited under the schemes had at least one major technical non-compliance, which the statement describes as an issue that will compromise the effectiveness of the insulation rather than pose a direct risk to safety1. A further 6% of EWI and 3% of IWI installations audited were categorised as posing potential risks to health or safety, and where such risks are identified installers are required to make them safe within 24 hours1.
"In October 2024, routine audits conducted by TrustMark, the independent body that oversees the quality of retrofit work done by tradespeople working in homes, identified significant levels of poor-quality solid wall insulation that had been installed under ECO4 and GBIS. TrustMark began to suspend installers, and the Department commissioned a much fuller audit."
| Measure | Audited installations with at least one major technical non-compliance | Audited installations posing potential health or safety risks |
|---|---|---|
| External wall insulation (EWI) | 92% | 6% |
| Internal wall insulation (IWI) | 27% | 3% |
The statement says installers are responsible for putting right any issues found with their work, and that no household should be asked to pay any money to put things right1. It adds that where the original installer is no longer trading, all works carried out under ECO4 and GBIS must be covered by guarantees, and householders can contact their guarantee provider1. The January 2025 statement said consumers did not need to take any action at that point, and that all households with solid wall insulation fitted under the schemes would be sent a letter from Ofgem within three weeks2.
Why it matters for households
Solid wall insulation is one of the measures intended to cut heat loss from a home that cannot be insulated through a cavity, and its performance depends on it being installed correctly. The audit results indicate that a large majority of the external wall insulation examined under these two schemes fell short of the technical standard required, which the statement says compromises effectiveness rather than posing a direct safety risk in those cases1. For a household, that can mean the expected reduction in heating demand does not materialise, so the energy independence the measure was meant to deliver is not achieved. A smaller proportion of installations were flagged as potential health or safety risks, with damp and mould cited among the consequences of poor work in the earlier statement2.
The statement says the issues were specific to solid wall insulation under ECO4 and GBIS, and that audits of the social housing decarbonisation fund, the home upgrade grant and the local authority delivery schemes showed no widespread problem, in part because those schemes are subject to more oversight and scrutiny1. Households with solid wall insulation under ECO4 or GBIS can contact Ofgem's contact centre by email at ECOhelD@ofgem.gov.uk, through a webform on gov.uk pages, or on freephone 0808 169 4447, Monday to Friday excluding bank holidays, from 9.30 am to 4.30 pm1.
What happens next
The Government is offering comprehensive on-site audits to every household with external wall insulation installed under the two schemes, at no cost to the consumer, with affected households initially contacted by Ofgem1. The Department will consult on proposals for a single system of oversight for retrofit work early next year, with further detail to be provided in the warm homes plan1. The statement says the Government retrofit system reform advisory panel will continue to support development of these proposals1.
Sources2 cited
- Retrofit Measures: ECO4 and GBIS - Hansard - UK Parliament, hansard.parliament.uk
- ECO4 and Insulation Schemes - Hansard - UK Parliament, hansard.parliament.uk