Ofgem’s supply chain rules for the Energy Company Obligation require installers delivering ECO4 measures to be a TrustMark registered business, with the sole exception of installers of district heating connections not connected to a shared ground loop.

Why TrustMark sits behind government schemes

TrustMark describes itself as the Government Endorsed Quality Scheme, and it sits behind a range of government-funded home improvement schemes, including ECO4 and the Boiler Upgrade Scheme, as the registration route that lets an installer legitimately deliver work funded under them. Choosing a TrustMark-registered business means engaging with an installer that has been vetted against required standards and has committed to a defined level of customer service, rather than relying purely on the installer’s own claims about its competence.

The narrow exception

Under ECO4 specifically, the requirement to be TrustMark registered applies to installers of almost every measure funded through the scheme. The one stated exception covers installers of district heating connections that are not connected to a shared ground loop; outside that specific category, TrustMark registration is a condition of delivering ECO4-funded work at all, not an optional quality mark an installer can choose to skip.

PAS 2030 and PAS 2035 alongside TrustMark

TrustMark registration does not stand alone. ECO4 adopts a whole-house approach to energy efficiency improvement, set out in Publicly Available Specification PAS 2035:2019, and projects involving the kinds of measures PAS 2035 covers are expected to follow its domestic retrofit process, including the involvement of a qualified retrofit coordinator overseeing how measures are assessed, designed and installed together rather than in isolation. Insulation and heating measures delivered under ECO4 generally also require installer certification to PAS 2030, alongside the TrustMark registration itself.

What TrustMark registration actually checks

TrustMark’s role is to confirm that a registered business has been assessed against the standards relevant to the work it carries out, giving a homeowner a way to verify that an installer offering grant-funded work is entitled to deliver it, rather than simply claiming to be. This matters specifically in a market where scam operators have targeted homeowners with offers of free or heavily discounted boilers and insulation under schemes like ECO4, since a genuine claim to be delivering scheme-funded work should be checkable against TrustMark’s own register rather than taken on trust from the installer alone.

Why this matters if you’re quoted for grant-funded work

If a quote for boiler or heating work is presented as funded, in whole or in part, through ECO4 or a similar government scheme, the installer, or the wider supply chain arranging the funding, needs to be operating through TrustMark registration for that funding route to be genuine. An offer of scheme funding from a business that cannot be found on the TrustMark register is a signal to check the offer carefully before agreeing to anything, rather than assuming the funding claim is accurate simply because it has been made.

Checking an installer yourself

TrustMark maintains a public search facility allowing a homeowner to look up whether a specific business is currently registered and which scheme categories it is registered to deliver, which is the direct way to confirm a claim of TrustMark registration rather than relying on a certificate or logo shown by the installer itself.

What happens if an installer isn’t registered

An installer that is not TrustMark registered simply cannot legitimately deliver work funded through ECO4 or the other government schemes that sit behind the register, whatever it claims in its marketing. Where a homeowner has already agreed to grant-funded work and later discovers the installer is not actually registered, that is a strong signal the funding arrangement itself may not be genuine, and it is worth pausing the work and checking directly with TrustMark or the scheme administrator before allowing any installation to proceed, rather than after the event.

FAQs

Does every ECO4 installer have to be TrustMark registered?

Almost every one; the only stated exception is installers of district heating connections not connected to a shared ground loop.

Is TrustMark registration the only standard an ECO4 installer needs?

No. Measures following PAS 2035’s whole-house retrofit process also generally require PAS 2030 installer certification alongside TrustMark registration.

How can I check if an installer is really TrustMark registered?

TrustMark maintains a public search facility that allows a business’s registration status to be checked directly, rather than relying on what the installer states.

Does TrustMark registration apply outside government-funded schemes?

TrustMark registration is specifically the route required to deliver work funded under schemes such as ECO4 and the Boiler Upgrade Scheme; an installer doing privately funded work outside these schemes is not required to hold it in the same way.

Bottom line

An installer delivering ECO4-funded boiler, heating or insulation measures must almost always be TrustMark registered, with a narrow exception for certain district heating connections, and often needs PAS 2030 or PAS 2035 standards alongside it. Checking a business against TrustMark’s own public register is the direct way to confirm a scheme-funding claim before agreeing to any work. This is general information, not advice on a specific quote; TrustMark’s register is the authoritative check for a particular installer.

Sources

This guide draws on the following primary sources, current as of 22 September 2026:

• Ofgem, “Energy Company Obligation (ECO) – Supply chain”
• TrustMark, “Government Schemes”

Related guides

Best Boiler Deals is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not regulated advice on any specific installation — always confirm the details with a Gas Safe registered engineer.