Replacing a gas boiler with a heat pump in London: the Boiler Upgrade Scheme, MCS installers and how to avoid being mis-sold

For most London homes, the boiler is the single largest piece of building services equipment, and replacing it is a decision that will shape running costs and comfort for many years. Heat pumps are now a mainstream alternative to a gas boiler, supported by a government grant in England and Wales. That combination - a substantial grant, a technology many households have never lived with, and installers competing for grant-funded work - is precisely where homeowners need to be most careful.

This guide explains how the grant works, what certifications genuinely protect you, what changed in planning law in 2025, and how to spot a mis-sold installation. It was checked against GOV.UK, Ofgem, MCS and legislation.gov.uk on 20 October 2026. Scheme rules change, so confirm current figures before you sign.

The Boiler Upgrade Scheme in brief

According to GOV.UK, the Boiler Upgrade Scheme (BUS) currently offers one grant per property:

• £7,500 towards an air source (air-to-water) heat pump;
• £7,500 towards a ground source or water source heat pump;
• £5,000 towards a biomass boiler;
• £2,500 towards an air-to-air heat pump.

Until March 2027, an additional £1,500 is available for air or ground source heat pumps where the property is heated by oil or LPG and has no mains gas connection - which Ofgem presents as a £9,000 grant for eligible off-gas-grid properties. Most London homes are on mains gas, so the standard figures will usually apply.

To be eligible, you must own the property (including a second home or a let property) and be replacing fossil fuel heating such as gas, oil, LPG or electric heating. Hybrid systems that pair a gas boiler with a heat pump are not eligible, and the installer must commission the system within 120 days of applying for the grant.

How the money is supposed to flow

The scheme is installer-led. GOV.UK sets out three steps: obtain quotes from MCS certified installers, confirm eligibility with your chosen installer, and agree a quote. The installer then applies to Ofgem on your behalf, and the value of the grant is taken off what you pay, shown on both quotation and invoice.

Ofgem's March 2026 summary of its installer guidance goes further: installers must pass the grant on as an upfront discount and must not request or accept the discounted amount from the property owner. Property owners, for their part, must confirm receipt of that discount. The practical rule is simple - you should never be asked to pay the grant amount yourself and "claim it back later".

Expect contact from Ofgem confirming that the installer is acting for you, and possibly a phone call or visit to check the installation. MCS may also carry out its own checks. A genuine installer will tell you this in advance.

Certifications that actually protect you

MCS certification

Only installers certified by MCS can apply for BUS grants. Ofgem notes that MCS sets the technical standards, certifies installers and products, and issues an MCS certificate for each completed eligible installation. Ofgem's guidance also says temporary MCS certification numbers are not acceptable for the scheme. Check the installer's certification number yourself on the MCS website rather than relying on a logo.

Consumer codes and deposit protection

MCS's Customer Commitment requires certified installers to give a clear written quotation, fair terms, transparent pricing, and to tell you how any deposit is protected; deposits must be reasonable and part of an agreed payment schedule. It also requires realistic, truthful performance estimates before you sign, and warns that you should not sign a contract based on specific energy tariffs, because tariffs vary and change.

For grant-funded work, Ofgem's guidance states that installers on the redeveloped MCS scheme must continue to belong to one of the two approved consumer codes - RECC or HIES - until further notice. Ask which code your installer belongs to and check it.

Building Regulations

Replacing a heating system is notifiable building work. GOV.UK's list of competent person schemes shows which bodies can self-certify heating, hot water and microgeneration work; an installer registered with one of them can certify compliance rather than you applying to building control. Under regulation 20 of the Building Regulations 2010, the installer must give you a copy of the compliance certificate and notify building control within 30 days of completion. If your old gas boiler is being removed, the gas supply must be safely disconnected by a Gas Safe registered engineer.

Planning: what changed in 2025

The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025 came into force on 29 May 2025 and loosened the rules for air source heat pumps. Its explanatory memorandum confirms that it:

• removed the requirement for any part of the unit to be at least one metre from the property boundary - significant for London's narrow terraces;
• increased the permitted outdoor unit size from 0.6 to 1.5 cubic metres for houses (flats remain at 0.6 cubic metres);
• allows up to two units on a detached house;
• allows units that heat and cool, but not those used solely for cooling.

The Planning Portal lists the limits that remain. Installations must comply with the MCS 020a sound calculation standard; units on pitched roofs are not permitted development; listed buildings fall outside the rights altogether; and in a conservation area the unit must not be on a wall or roof fronting a highway, or nearer to the highway than the house itself. Permitted development rights can also be removed by an Article 4 direction or planning condition. Given how much of inner London lies in conservation areas, ask your borough before you commit.

London-specific considerations

• Flats and leasehold. Even where planning rules allow a unit, your lease will very often require the freeholder's written consent for external alterations. Obtain it before paying a deposit.
• Space for a cylinder. Homes moving from a combination boiler typically need room for a hot water cylinder, which can be the deciding factor in a small London flat. A proper survey should address this before quoting.
• Neighbours and noise. With the one-metre rule removed, units can now sit close to a neighbour's window. The MCS 020a calculation is there to protect neighbours, so ask to see it.
• Party walls. Fixing a unit or brackets to a shared wall may raise party wall questions; discuss this with the installer and, if needed, your neighbour.

Red flags of heat pump mis-selling

• being asked to pay the grant amount up front, or to sign a form you have not read "for the grant";
• a quotation that does not show the grant deducted, or an invoice that differs from the quote;
• no heat loss survey, or a system sized from the old boiler's output alone;
• savings projections tied to a particular energy tariff, which the MCS Customer Commitment specifically warns against;
• a "temporary" MCS number, or a certification number that does not match the company on the paperwork;
• no clear answer about which consumer code the installer belongs to, or how your deposit is protected;
• doorstep or cold-call offers of a "free" heat pump with pressure to sign the same day.

If you sign a contract at home, the Consumer Contracts Regulations generally give you 14 days to cancel. For contractual disputes, the installer's consumer code and MCS each provide a complaints route; Ofgem investigates suspected fraud relating to the scheme.

A sensible order of events

1. Confirm your borough's planning position, and any leasehold consent, before inviting quotes.
2. Invite at least three MCS certified installers to survey the property properly.
3. Compare quotes on the heat loss survey, the specified unit and cylinder, radiator changes, the grant deduction and the deposit protection.
4. Check MCS certification, consumer code membership and Companies House records for the firm you prefer.
5. Pay a modest, protected deposit; never the grant amount.
6. At handover, collect the MCS certificate, the Building Regulations compliance certificate, the commissioning record and the warranty documents.

Sources (checked 20 October 2026): GOV.UK, Apply for the Boiler Upgrade Scheme; Ofgem, Boiler Upgrade Scheme; Ofgem, summary of BUS installer guidance v5 (March 2026); MCS Customer Commitment; GPDO Amendment Order 2025, article 5; Planning Portal, Air source heat pumps; GOV.UK, Competent person schemes; Building Regulations 2010, regulation 20. Nothing here is financial or legal advice.