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How to find an ECO4 installer, and how to check one

ECO4 Application is an independent information and eligibility-check site. We are not the government, Ofgem, an energy supplier, a council or an installer. We do not have installer partners and we do not recommend firms. What we can do is show you where official lists are and what an ECO4 installer must have, from Ofgem's ECO4 delivery guidance (version 4.0).

In short: ECO4 runs until 31 December 2026 (Ofgem). Start from an obligated energy supplier (Ofgem publishes the list) or your council's ECO4 Flex scheme, and check any installer on the TrustMark register. ECO4 work must be done by, or under, a TrustMark-registered business certified to PAS 2030:2023 and delivered under PAS 2035:2023 with a Retrofit Coordinator.

Sources: Ofgem, ECO4 Guidance: Delivery v4.0 (26 Mar 2026), paras 4.9-4.19 and 5.254-5.266; Ofgem, homeowners and tenants. Checked 31 October 2026.

Where to start

Starting pointHow it works
An obligated energy supplierOfgem says you can contact any of them, not only your own; it publishes their contact details
Your council (ECO4 Flex)Councils that take part publish a Statement of Intent on their website; many say how to apply
An installer who approached youAsk which supplier funds the work; check them on TrustMark and with the supplier

Ofgem's contact list is on its ECO contacts and guidance page.

What a legitimate ECO4 installer must have

  • TrustMark registration for the measure being installed. Ofgem says measures installed to PAS or MCS standards must be installed by, or under, a TrustMark-registered person, and non-compliant work is rejected.
  • PAS 2030:2023 certification (or MCS for microgeneration such as solar PV or heat pumps), from an accredited certification body.
  • PAS 2035:2023 delivery, managed by a qualified Retrofit Coordinator, who oversees the risk and dwelling assessment, design, installation and monitoring.
  • Guarantees that meet TrustMark's framework; TrustMark lists appropriate 25-year guarantees on its website.

Questions to ask any installer

  1. Which obligated supplier is funding this job?
  2. What is your TrustMark registration, and does it cover this measure?
  3. Who is the Retrofit Coordinator?
  4. Which guarantee will I receive, and from whom?
  5. Will I be asked to contribute anything? (Ofgem says this can happen.)

After the work

Keep the guarantee and any Unique Measure Reference. GOV.UK says to take problems to the installer or the guarantee provider first, then Citizens Advice; TrustMark also runs a complaints process. Read is ECO4 legit for warning signs, and how to apply for ECO4 for the full process.

Why we don't recommend installers

This site is independent and has no installer partner. If you use our checker, we reply by email with the route and official contacts that fit your answers.

Questions

How do I find an ECO4 installer?

Ofgem says you can contact any obligated energy supplier, and it publishes their contacts. You can also check any installer on the TrustMark register, which ECO4 installers must be on.

What accreditation does an ECO4 installer need?

Ofgem's delivery guidance says ECO4 measures must be installed by, or under, a TrustMark-registered business certified to PAS 2030:2023 (or MCS for microgeneration) and delivered within PAS 2035:2023.

What is a Retrofit Coordinator?

Under PAS 2035, a qualified Retrofit Coordinator oversees the project from assessment and design to installation and monitoring.