Installers

Home Energy Installers and Retailers: The Full UK Guide to Hiring, Checking and Complaining

Anyone in the UK who wants a new boiler, a heat pump, solar panels, insulation or a home chargepoint faces the same two questions before anything else: who is allowed to do this work, and who is standing behind them if it goes wrong. The answers sit in a layered system of registration schemes, certification bodies and consumer codes that most householders never see until something breaks. This guide sets out that system in full: what TrustMark, MCS, NICEIC and the consumer codes each cover, what a competent person scheme means for your Building Regulations paperwork, what warranties and guarantees come with certified work, and exactly how a complaint travels from your installer to the Energy Ombudsman.

The headline rules are simple. Installers working under UK Government schemes must be TrustMark registered and/or MCS certified¹. MCS installation companies working with domestic customers must also belong to a consumer code approved by the Chartered Trading Standards Institute². TrustMark registered businesses must give a minimum two-year warranty on their work, and certain measures installed under the Energy Company Obligation carry a minimum 25-year guarantee¹. Beyond that, the detail matters: which scheme covers which technology, what certification actually promises, and where the boundaries of redress lie.

Who checks an installer: the four layers of oversight

No single body vets every tradesperson who works on a home. Instead, oversight comes in layers, and knowing which layer applies to your job is the first step in checking anyone.

The top layer is government endorsement. TrustMark is a government endorsed quality scheme covering work in and around the home⁷, and it is the entry requirement for a growing share of funded work. The Warm Home Discount (England and Wales) Regulations 2026 require that a boiler or central heating system is installed by, or under the responsibility of, a person registered with TrustMark, with a certificate of lodgement issued by the operator of TrustMark¹⁰. Council-run grant programmes apply the same test: the installers on Surrey County Council's Warm Homes Local Grant network are TrustMark Registered, MCS accredited for renewable technologies and certified to PAS 2035:2023¹¹.

The second layer is technology certification. MCS, the Microgeneration Certification Scheme, is a certification scheme for microgeneration installation companies and products, covering small-scale renewable technologies of 50kW or smaller³. The third layer is trade certification for the underlying craft, such as NICEIC registration for electrical businesses. The fourth layer is the consumer code: a CTSI-approved code of practice that certified installers must join before they can work with domestic customers, and which governs how they sell, contract and handle complaints⁹.

Crucially, these layers also police themselves after the job. MCS undertakes its own checks on installations completed by MCS-certified installers, separate from Ofgem's audit programme, and may contact owners directly or arrange a visit¹². Our detailed pages on MCS certified installers, TrustMark registered businesses and NICEIC registered electricians unpack each layer in turn.

TrustMark: the official quality standard for tradespeople working on your home

TrustMark occupies a distinctive position because it is the only scheme in this system with direct government endorsement⁷. That endorsement is not a vague badge of honour. It is written into the rules of funded schemes, which makes TrustMark registration a practical gate on who can carry out certain work at all.

The clearest example is in legislation. Under the Warm Home Discount (England and Wales) Regulations 2026, a boiler or central heating system installed under the scheme must be fitted by, or under the responsibility of, a person registered with TrustMark, and a certificate of lodgement must be issued by the operator of TrustMark¹⁰. That certificate of lodgement is a formal record that the job was done by a registered business, and it is paperwork a householder can expect to see.

Local authority grant schemes apply the same standard. Bristol City Council's grant and loan programme for home energy efficiency points householders to TrustMark as the quality scheme behind the installers it funds⁷, and Surrey County Council requires its Warm Homes Local Grant installers to be TrustMark Registered alongside MCS accreditation and PAS 2035:2023 certification¹¹. Birmingham City Council's ECO4 and GBIS Flex statement of intent names the approved installers delivering the scheme, including City Energy Network Ltd and Next Energy Solutions Ltd, both described as TrustMark-registered ECO and GBIS installers¹³.

TrustMark also carries consumer-facing obligations that matter after the work is done:

• Registered businesses must provide a minimum two-year warranty for work¹.
• A minimum 25-year guarantee applies to certain measures installed under the Energy Company Obligation¹.
• A dedicated complaints route exists for customers of registered businesses, covered in more detail on how to complain about a TrustMark registered business.

MCS: the quality mark for small-scale renewables

MCS is the certification scheme for microgeneration installation companies and products, and it aims to ensure consistent standards and provide confidence to consumers². Its scope is defined by size: MCS is the leading quality assurance organisation for microgeneration, meaning small-scale renewable technologies of 50kW or smaller³. In practice that covers the technologies most households install: heat pumps, solar photovoltaic panels, batteries and related equipment.

Certification is not a one-off badge. MCS's roles include:

• Setting and maintaining technical standards for installations and products
• Certifying installers and products against those standards
• Issuing MCS certificates for completed eligible installations
• Assisting certification bodies to review and address cases and consumer issues relating to installers or products¹⁴

The certificate issued at the end of a job is therefore not a courtesy document: it is the record that the installation was completed by a certified installer to MCS standards, and it is what grant schemes look for. The Boiler Upgrade Scheme guidance for property owners notes that MCS also undertakes its own checks on installations completed by MCS-certified installers, and may contact owners directly or arrange a visit¹⁵.

MCS certification is also a condition of access to grant funding. The Boiler Upgrade Scheme, which provides grants towards heat pump installations, is built around MCS-certified installers and MCS certificates, and Ofgem's guidance for both installers and property owners sets out the certification requirements in detail¹⁶. Our pages on the MCS installation standards, your MCS certificate and handover documents and installer requirements for grants cover what certification demands of an installer in practice.

One point of transition is worth noting. Installers who have not yet moved to the MCS Redeveloped Installer Scheme must still hold consumer code membership with one of the other two approved codes of practice, HIES and RECC¹⁶. The consumer protection does not lapse while the scheme changes.

NICEIC: Britain's biggest assessor of electricians

Behind most solar, battery and chargepoint installations there is electrical work, and NICEIC is the certification body most householders will encounter. NICEIC-registered electricians are businesses, not individuals, and the registration carries three protections worth knowing about.

First, assessment is continuous: a NICEIC-registered electrician's business is assessed annually by an experienced NICEIC assessor to ensure it meets stringent quality and technical requirements⁸. Second, the business must hold comprehensive insurance to protect you and your property in the unlikely event of accidental damage or injury⁸. Third, the work is backed by NICEIC's Platinum Promise guarantee⁸, a workmanship guarantee that sits behind the installer's own warranty, and which is explained in detail on what the NICEIC Platinum Promise covers.

For a householder, the practical significance is that electrical registration is checkable before you sign. NICEIC's own guidance on choosing an electrician sets out these three protections as the reason to use a registered business⁸, and registration can be confirmed through the routes described on how to verify an electrician is registered. NAPIT operates a parallel registration system for the same kinds of work, covered on NAPIT registration: schemes, scope and checking an installer, and the choice between them is a matter of which scheme the business joined, not of differing legal status.

Registration also connects to the wider system in this guide. Electrical work in a home falls under Building Regulations, and registered electricians can self-certify that work, which removes the need for a separate building control application. That mechanism, and when the law requires a qualified electrician, is covered on who can self-certify electrical work in a home and when you need a qualified electrician by law.

RECC and HIES consumer codes: rules in flux

Certification tells you an installer is technically competent. A consumer code tells you how they must behave when they sell to you, take your deposit and handle your complaint. This is the layer that turns a technical standard into consumer protection.

The rule is unambiguous. A requirement of companies wanting to gain MCS certification is that they are members of a CTSI Approved Consumer Code of Practice scheme in the first instance⁹. Ofgem's guidance states the same from the other direction: MCS installation companies working with domestic customers must also be a member of a Consumer Code approved by the Trading Standards Institute². The Boiler Upgrade Scheme guidance for property owners puts it plainly: "A condition of MCS certification is membership to HIES or RECC."¹⁷

The two codes named are the Renewable Energy Consumer Code and the Home Insulation & Energy Systems Quality Assured Contractors scheme. The RECC was developed and is sponsored and run by Renewable Energy Assurance Ltd (REAL)⁹, and it can be reached on +44 (0)207 981 0850². Both codes govern selling practices, contract terms, deposit protection and complaints handling, and both are compared in detail on RECC and HIES compared: two consumer codes for energy installations, with the individual codes covered on the Renewable Energy Consumer Code and the HIES consumer code.

The requirement is currently in transition alongside the MCS Redeveloped Installer Scheme. Installers who have not transitioned to the new scheme must still hold consumer code membership with one of the other two approved codes of practice, HIES and RECC¹⁶. For a householder, the practical check is simple: whichever code your installer belongs to, membership can be confirmed before you sign, and the code is the first port of call for a complaint about selling or contract conduct, as described on how to complain to the Renewable Energy Consumer Code.

How competent person schemes relate to Building Regulations

Every installation in this guide touches Building Regulations: a boiler, a heat pump, electrical work, ventilation. The question of who certifies compliance is separate from who certifies competence, and competent person schemes are the mechanism that joins the two.

A competent person scheme allows approved installers who join one to self-certify certain types of building work¹⁸. Membership is voluntary for installers¹⁸, but the practical effect of not joining is significant: an installer not in an approved competent person scheme will not be able to self-certify that their work is compliant¹⁹. In that case the householder must arrange separate building control approval and inspection, which adds cost and delay to the job.

The government's Future Homes and Buildings Standards work has sharpened this link. The consultation response records that significant amendments were made to the Approved Documents to state that a competent person scheme is to be used when undertaking a heat pump or mechanical ventilation installation²⁰. For installing mechanical ventilation and air conditioning systems in dwellings, there are currently four registered competent person schemes²⁰.

For a householder, the significance is paperwork. Work self-certified by a scheme member generates a Building Regulations compliance certificate, explained on what a Building Regulations compliance certificate is for, and the schemes themselves are mapped on competent person schemes: which installers can self-certify their own work. The position is the same across England and Wales in principle, though Welsh guidance on building regulations for boilers and heating sets out the position for Welsh households separately¹⁹.

From two-year work warranties to 25-year ECO guarantees

The protection that matters most after an installation is the written warranty on the work and the guarantee on the measure. These are not marketing extras: for TrustMark registered businesses and ECO-funded work, they are minimum standards.

TrustMark registered businesses must provide a minimum two-year warranty for work, and a minimum 25-year guarantee applies to certain measures installed under the Energy Company Obligation¹. The 25-year figure reflects the nature of insulation measures, where defects can take years to surface, and it is the longest guarantee in the domestic energy system.

Outside the funded schemes, workmanship guarantees vary by installer. Installer workmanship guarantees typically last between 1 and 10 years, with MCS-certified installers required to offer a minimum of two²¹. That means the two-year floor follows the MCS certification into the open market, not just grant-funded work: an MCS-certified installer quoting a one-year workmanship guarantee is quoting below what their certification requires.

A workmanship guarantee is only as good as the business standing behind it, which is why many installers also offer insurance-backed guarantees, covered on what an insurance backed guarantee (IBG) is and when you need one and insurance-backed guarantees on energy installations. The related questions, how deposits are protected and what happens to a guarantee when an installer stops trading, are covered on deposits and staged payments and what to do if your installer has stopped trading.

The limits of what MCS certification assures

MCS certification is often described as a promise that an installation will perform. The scheme's own scope is narrower than that, and householders are better served knowing exactly where the promise ends.

What MCS does is set and maintain technical standards for installations and products, certify installers and products against those standards, issue MCS certificates for completed eligible installations, and assist certification bodies to review and address cases and consumer issues relating to installers or products¹⁴. That is a standards and certification role, not a performance guarantee role.

The limits are stated plainly in the government's heat pump transition report:

And further:

A householder whose heat pump uses more electricity than the installer's prediction predicted cannot treat MCS certification itself as the remedy. The design-stage prediction is a document to scrutinise before signing, not a warranty to fall back on afterwards, and what it must show is covered on what an MCS performance estimate must show.

There are technical boundaries too. MCS's standards govern the installation as designed, and third party non-modulating controls are not prohibited²², so the presence of the certificate does not tell you everything about the control setup. What the certificate does give you is a verifiable record of who installed what, to which standard, on which date, and that record is what unlocks grant funding and underpins any complaint.

If an installer fails you: complaining via MCS and TrustMark

When an installation goes wrong, the complaint route depends on which layer of the system the problem sits in.

The escalation path runs in order:

1. Complain to the installer first.
2. If the complaint is not resolved, approach the MCS Administrator, who will advise how to make a complaint about the MCS installer²³.
3. In parallel, the consumer code handles selling and contract disputes, and TrustMark's own complaints process covers its registered businesses, described on how to complain about a TrustMark registered business.

MCS's post-installation checks can also work in the householder's favour. MCS undertakes its own checks on installations completed by MCS-certified installers, separate from Ofgem's audit programme, and may contact owners directly or arrange a visit¹². If MCS contacts you about a check on your installation, the installer guidance asks property owners to aim to respond within seven days²⁴. Cooperating with these checks is one of the few ways the system actively inspects finished work rather than relying on householders to report problems.

For a fuller picture of what can go wrong and how defects are put right, see when an installation goes wrong: common defects and remediation and complaining about an installer: the escalation route.

Taking a dispute further: the Energy Ombudsman, eight weeks to verdict

Some disputes cannot be resolved with the installer, the consumer code or the certification body. Where the dispute involves an energy supplier, an energy broker, a network operator, a Green Deal or heat network supplier, the final stage is the Energy Ombudsman, an independent service approved by Ofgem to handle service disputes in the energy sector²⁵.

The Ombudsman cannot be reached on day one. Before raising a dispute, you must have allowed the supplier 8 weeks to resolve it, or have received a Deadlock Letter allowing you to escalate earlier⁴. The eight-week rule is consistent across the schemes the Ombudsman covers: Ofgem's guidance confirms that if after 8 weeks your issue is still unresolved, the Ombudsman can then investigate²⁵, and the same eight-week period applies to heat networks²⁷, to Green Deal complaints in England and Wales¹, and to domestic Feed-in Tariff generators, who can refer a dispute after 8 weeks from the complaint being lodged if no mutually agreeable outcome has been reached²³. A deadlock letter allows you to come to the Ombudsman sooner than 8 weeks²⁸.

Once a case is open, the process has a defined shape. The Ombudsman will ask you to send information and evidence, review evidence from you and your energy company, inform you of their decision within 6 weeks, and give the energy company a set of actions to resolve the problem⁶. On average, most disputes are resolved within 6 weeks of the Ombudsman receiving evidence from both parties⁵. The waiting periods are unpacked on how long before you can take a complaint to the Energy Ombudsman.

The Energy Ombudsman's powers and their limits

The Energy Ombudsman can order real remedies, but it is not a regulator and it is not a court. Knowing the difference prevents a common disappointment.

What it can do: the Ombudsman can tell suppliers to take practical action, such as crediting or cancelling an account or changing your tariff, make an apology, or offer a financial award, or a combination of these, and it may make recommendations to prevent issues happening again⁵. Financial awards are based on the cost of putting things right, such as ensuring you have been charged accurately, clearing unfair charges or fixing faults⁵. For domestic disputes the maximum is up to £10,000, and up to £20,000 for small business disputes, though the level of maximum financial award may vary depending on the type of energy company and the Terms of Reference that cover that scheme⁵. The average award is around £50⁶.

What it cannot do: the Ombudsman cannot punish companies, dictate how companies operate, or issue fines⁵. As its own guidance puts it:

The scope is broad but bounded. The Ombudsman handles disputes involving energy suppliers, energy brokers, network operators, Green Deal and heat network suppliers³⁰. Heat network disputes have been handled since 1 April 2025, and disputes for a number of flexibility service providers since 8 January 2026³¹. Network operator disputes are considered where there is a loss of service or a problem with a connection or repair²⁸. The Ombudsman can consider complaints about EV charging at a consumer's home, but not charging away from the home³². It only handles disputes involving suppliers trading in Britain²⁵, and other sectors such as travel, retail, insurance, employment, financial products or banking are covered by other ombudsman schemes, of which there are over 20 in the UK³³. Eligibility for businesses is defined by size thresholds: a microbusiness, for example, is one with annual electricity consumption of not more than 100,000 kWh or gas consumption of not more than 293,000 kWh, and not exceeding £2 million annual turnover²⁵.

Deadlines and dates that affect your installation

Several dates in the current programme shape what installers can offer and what householders can claim.

The Energy Company Obligation has been extended to 31 December 2026 to meet existing targets and remediate non-compliant installations¹. ECO4 obligates the larger energy suppliers to deliver a target of annual bill savings by installing energy efficiency and heating measures to homes, across Great Britain³⁴. The technical standards behind that work are set out in the legislation: PAS 2030:2023, Incorporating Corrigendum No. 1, Installation of energy efficiency measures in existing dwellings, and PAS 2035:2023, Incorporating Corrigendum No. 1, Retrofitting dwellings for improved energy efficiency, both published by the British Standards Institution in 2024³⁵. These standards are why ECO and GBIS installers, like those named in Birmingham City Council's statement of intent, are TrustMark-registered and certified to PAS 2035¹³.

The Future Homes and Buildings Standards programme is changing what new homes require and how installations are certified. The consultation response records that Approved Documents have been amended to state that a competent person scheme is to be used when undertaking a heat pump or mechanical ventilation installation, and that there are currently four registered competent person schemes for mechanical ventilation and air conditioning systems in dwellings²⁰. VAT on energy-saving installations is covered in detail on VAT on home energy installations.

The statistical backdrop is also on a schedule. The ONS energy efficiency of housing release for England and Wales was published on 6 October 2025, with the next release in October 2026³⁶, and its heat pump dataset is maintained by the Housing Analysis team²². For a householder, these dates matter less than the scheme deadlines, but they mark the pace at which the installation market is changing.

Where to buy and who fits: national companies, web retailers, merchants and local firms

The firms that sell and install home energy equipment arrive at your door through several different channels, and the channel shapes what protection applies.

At the funded end, local authorities and their delivery partners appoint approved installers. Birmingham City Council's ECO4 and GBIS Flex statement of intent names its approved installers, with City Energy Network Ltd contactable at BCC-ECO@cityenergy.co.uk and Next Energy Solutions Ltd at bcc@nextenergyuk.co.uk, both TrustMark-registered ECO and GBIS installers¹³. Surrey County Council's Warm Homes Local Grant network likewise uses installers who are TrustMark Registered, MCS accredited and certified to PAS 2035:2023¹¹. In these cases the householder's protection starts with the council's own scheme rules.

In the open market, the choice is between national installers operating across the UK, online fixed-price sellers, builders' merchants supplying kit, and local certified firms. Whichever channel is used, the certification checks in this guide do not change: an MCS-certified installer must offer a minimum two-year workmanship guarantee²¹, and MCS-certified installers are subject to MCS's own installation checks¹². Guidance on choosing a solar panel installer emphasises the same point from the buyer's side: check certification, check the guarantee period, and check the consumer code before signing²¹. The channels are compared on national installer or local firm: how the two compare, national home energy installers, online fixed-price installation and builders' merchants and trade retailers.

The impact on how self-sufficient your home's energy is

The installer and retailer system exists to make household energy independence safe and enforceable, and it largely succeeds: certification, consumer codes, warranties and ombudsman redress mean a householder installing a heat pump or solar panels is not relying on goodwill alone. A certified installation with a lodged certificate, a two-year workmanship warranty and a consumer code behind it is a genuine asset, and the strongest protections in the system, the 25-year ECO guarantee and the TrustMark lodgement requirement, attach to exactly the measures that reduce a home's dependence on imported energy¹.

The dependence that remains is worth stating plainly. An MCS certificate does not verify actual performance, and MCS does not require remediation of systems underperforming relative to their design²², so the running savings promised at design stage rest on the installer's competence and your own scrutiny of the prediction. The Energy Ombudsman cannot punish companies or issue fines⁵, so redress is remedial, not punitive. Grant-funded work depends on scheme deadlines, with ECO4 closing on 31 December 2026¹. And every installation still connects to something outside the home: the grid, a supplier, a certification body, a manufacturer's warranty. The system described here reduces the risk in becoming self-sustaining; it does not remove it, and the householder who checks registration, reads the guarantee and keeps the paperwork is the one who keeps the independence they paid for.