Heat pump warranties and complaints: who must put things right?

What to know first

This summary explains how the main protections fit together when a domestic air source heat pump develops a fault or performs poorly.

Heat pump disputes can become confusing because several protections may cover different parts of one system. Citizens Advice’s May 2026 analysis found that problems were most commonly raised during ongoing use, after installation. Some consumers also struggled to get an installer or manufacturer to put matters right.

In practice, responsibility follows the cause of the problem and the contract. The installer is usually the first contact, but a product defect may also engage the manufacturer’s warranty. Financial protection matters mainly if the installer has stopped trading or will not carry out required remedial work.

Who is responsible when a heat pump goes wrong?

This table is a starting point. The contract, warranty wording and technical evidence will decide the route in an individual case.

The matrix reflects current MCS installer responsibilities, general consumer-law principles and the separate role of product and financial protections.

For MCS-certified work, the certified installer remains responsible for the contracted installation and issues within MCS scope. That does not change because a subcontractor carried out the work. Consumer law also generally directs the household back to the trader that arranged it.

A warranty is an extra contractual promise with its own conditions. It does not replace rights against the trader when goods are faulty or services were not carried out with reasonable care and skill.

What does each heat pump protection cover?

Manufacturer or product warranty

This concerns the equipment listed in the terms. The document may promise a repair, replacement or another remedy, but labour and call-out costs should not be assumed. Check the duration, registration deadline, exclusions, approved-engineer rules, servicing conditions and whether the cover transfers when a home is sold.

The installer should provide the manuals and relevant warranties. An MCS installer must also explain anything the customer needs to do to validate or maintain them.

Installer design and workmanship guarantee

This concerns what the installer designed and built. It may apply where the heat pump is the wrong size, emitters or controls are unsuitable, pipework or wiring is defective, or commissioning and handover were incomplete.

Under the redeveloped MCS scheme, a domestic customer must receive written guarantees for system design and installation workmanship. The certified installer remains responsible for its contracted and certified work.

Financial protection or insurance-backed guarantee

This is a backstop, not a duplicate product warranty. Current redeveloped MCS protection must be able to fund remedial work if the installer ceases trading or refuses remediation required through the MCS complaint or dispute-resolution process.

It must last at least six years after certification, transfer on a home sale and cap any excess at £250. Permitted exclusions can include wear and tear, claims belonging solely under a manufacturer’s guarantee and defects caused by failure to follow clearly explained maintenance requirements.

Older installations may have different terms because their contracts were made under an earlier scheme version. The individual protection certificate therefore remains decisive.

Expert insight

“Do not compare protections only by length. Identify what failed, what the contract promised and whether the issue concerns the product, design, installation or later maintenance.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

Can missed servicing invalidate a heat pump warranty?

Potentially, but the written terms matter. Energy Saving Trust says servicing should follow the manufacturer’s advice, usually once a year. The MCS handover pack should state the recommended schedule and explain how to keep protections valid.

A missed service does not prove that every later fault is excluded. Check whether the condition was made clear and whether the defect is connected to poor maintenance. MCS financial-protection rules permit a maintenance exclusion where the manufacturer’s requirements were explained to both installer and customer.

Good to know

A maintenance plan is separate from a warranty. Check the required service interval and engineer qualifications before buying an optional plan. Government consumer guidance says households should not feel pressured into purchasing extra aftercare immediately.

What evidence should you keep if performance is disputed?

Keep evidence of what was promised, how the system was designed, what happened and how the installer responded. MCS asks complainants for details, photographs and documents such as the contract, quotation and system performance estimate.

1. Contract and quotation: signed terms, specification, price and written variations.

2. Design records: heat-loss calculation, system design, performance estimate and stated assumptions.

3. Handover documents: manuals, commissioning data, MCS certificate and relevant compliance documents.

4. Protection records: warranty registration, guarantees, financial-protection certificate and service invoices.

5. Fault timeline: dates, error codes, settings, temperatures, loss of heat or hot water, photographs and videos.

6. Correspondence: emails, letters, call notes, reports, invoices and the remedy requested.

The MCS Customer Commitment requires the handover pack to include the recommended maintenance schedule, manufacturer manuals and relevant guarantees. It also requires the MCS certificate and certain compliance documents to be provided within 30 calendar days of completion.

As a practical matter, household bills alone may not prove that an installation breaches its contract. Weather, settings, energy tariffs and household use can affect consumption. Compare actual operation with the pre-sale design and performance information. MCS financial protection may exclude compensation for expected bill savings while still funding work needed to bring an installation into line with its contracted design.

How do I complain about a heat pump installation?

1. Write to the contracting installer. Explain the fault, when it began, its effect and the outcome sought. Attach the most relevant evidence. MCS requires the installer to have the first opportunity to investigate and respond.

2. Ask for a written plan. An installer operating under the MCS Customer Commitment should acknowledge the complaint within two working days. MCS says 14 days is a reasonable maximum for a response. Repair may take longer, but there should at least be an agreed action plan.

3. Allow reasonable access. Record appointments, findings, missed visits and proposed repairs. MCS expects a complainant to allow the installer access to carry out appropriate remediation.

4. Escalate to MCS. Its policy covers matters including design, performance, workmanship, incomplete work, commissioning, handover, property damage, mis-selling and contractual issues where the installer was appropriately certified when contracted. A complaint solely about an MCS-certified product normally starts with the manufacturer and product certification body.

5. Use the applicable dispute route. Eligible cases under the redeveloped scheme can use independent alternative dispute resolution funded by MCS. A contract made from 1 January 2025 under the old scheme may also be referred if the installer agrees to be bound by the outcome; earlier contracts normally retain their consumer-code route.

   Since 20 January 2026, new complaints about Renewable Energy Consumer Code members have gone to Green Homes Dispute Resolution. HIES says its members’ customers can access mediation and a free ombudsman or equivalent dispute-resolution service.

6. Get independent advice where needed. MCS focuses on securing a functioning, compliant installation and says it cannot make an installer pay compensation. Consumer help is available through Citizens Advice in England and Wales, Advice Direct Scotland in Scotland, and Consumerline in Northern Ireland.

MCS states:

As at 19 August 2026, MCS certification bodies are moving installers to the redeveloped scheme until 31 March 2027. Consumer-code membership was mandatory under the old scheme but is voluntary under the redeveloped scheme. The route depends on the scheme version that applied when the contract was made, rather than simply the complaint date.

What happens if the installer has stopped trading?

A manufacturer’s warranty may remain valid when the seller or installer has closed. Contact the manufacturer with proof of purchase, registration and fault details.

For design or workmanship problems, check the financial-protection or insurance-backed guarantee certificate. Redeveloped MCS protection covers installer failure and must last at least six years after certification.

Older protections vary. HIES, for example, says its insurance-backed guarantees run for two to 10 years and may not match the installer’s own written guarantee.

An independent heating engineer may help identify a disputed cause. Check with the installer, manufacturer or protection provider before making major alterations, because a modification that causes a defect can affect financial-protection cover. Current MCS rules preserve cover for reasonable emergency repairs needed to protect the property or limit loss.

Consumer or legal advice may be appropriate where the dispute concerns compensation, consequential loss or a contract outside MCS.

Key takeaways

• Start with the business named in the installation contract.

• Product, design, workmanship and financial protections are separate.

• The MCS-certified installer remains responsible for contracted work, including subcontracted work.

• Follow written servicing conditions and keep proof.

• Preserve the design, handover, warranty, service and complaint records.

• Escalation depends on the contract date, scheme version and any consumer-code membership.

• No warranty or complaint route guarantees compensation or a particular technical outcome.

Frequently asked questions