Boiler Upgrade Scheme (BUS)

The Boiler Upgrade Scheme is the simplest of the major UK home energy grants in design — a flat voucher applied to a single measure. But the rules around who can install, what counts, and how the voucher flows trip up most first-time applicants.

For a typical household swapping a gas boiler for an air source heat pump, BUS reduces an £11,000 installation to around £3,500 to £5,000 net. For households on oil or LPG it often makes the heat pump the lowest lifetime-cost option already.

What BUS actually is

The Boiler Upgrade Scheme is a Treasury-funded grant administered by Ofgem under the Domestic Renewable Heat regulations. It launched on 23 May 2022, replacing the Renewable Heat Incentive (RHI). Unlike RHI, which paid quarterly tariff payments over seven years, BUS is a single up-front voucher.

The scheme covers England and Wales only. Scotland has the Home Energy Scotland Grant and Loan, with broadly equivalent values; Northern Ireland has separate arrangements.

From October 2023 the heat pump voucher value rose from £5,000 (ASHP) and £6,000 (GSHP) to a flat £7,500. In March 2026 the Treasury extended BUS funding through to 2028 and confirmed the £7,500 rate is held — though the consultation is open on a tiered structure for 2027 onwards.

What BUS pays for

Hybrid heat pumps (heat pump plus a back-up gas boiler) were excluded from BUS in 2023 and remain excluded. Air-to-air systems (units that produce hot air rather than hot water through radiators or underfloor heating) are not eligible. Shared ground loop systems on small rural sites can be eligible under specific MCS rules.

Who is eligible

Eligibility is property-based, not income-based. There is no means test.

The "off-gas" requirement that applied in older grant schemes does not apply under BUS. A household on mains gas can replace its gas boiler with a heat pump and still claim the £7,500.

How the voucher flows

This is the part that confuses most households. The household never sees the £7,500 directly.

1. Installer survey and quote. An MCS-certified installer surveys the property, calculates heat loss, sizes the heat pump, and produces a quote. The quote shows the gross price, the BUS voucher, and the net price the household pays.
2. Voucher application. The installer applies to Ofgem on the household's behalf, with the household countersigning. Ofgem confirms the voucher within 10 working days.
3. Voucher issue. Once issued, the voucher is valid for three months for ASHP and biomass, six months for GSHP. The install must be commissioned in that window.
4. Install and commission. Installer fits the heat pump, commissions it, registers the install with MCS.
5. Voucher redemption. Installer submits the redemption claim to Ofgem. Voucher value is paid to the installer. Household pays only the net balance from the original quote.

Some installers ask the household to pay the gross amount up front and then receive a reimbursement once the voucher is paid. This is a red flag — the standard model is for the household to pay the net amount only. If an installer insists on full payment up front, ask why.

What to ask installers for

The MCS certification process is robust on the technical side but light on commercial protection. Households who want a clean install should ask for the following before signing:

• Heat loss calculation per room — at minimum a CIBSE TM59 or MCS heat loss form, not a rule-of-thumb estimate.
• Specified heat pump model from the MCS Product Database, with SCOP at the design flow temperature (35°C, 45°C, 55°C).
• Radiator schedule with sizes and required upgrades — most homes need at least two radiators upsized.
• Cylinder spec — most heat pump installs replace the cylinder. Volume should be at least 200 litres for a family home, with an immersion as back-up.
• Buffer tank or volumiser only if needed — many installers add unnecessary buffer tanks. Ask why.
• Hydraulic schematic showing the system layout.
• Estimated annual running cost at typical UK weather, with the assumed unit rate for electricity and the assumed thermostat schedule.
• Workmanship warranty — minimum two years on labour, manufacturer warranty (typically 5-7 years) on parts.
• MCS certificate and heat pump warranty registration both included in the documentation pack handed over on commissioning.

If the installer refuses to provide the heat loss calculation or the SCOP figure for the proposed flow temperature, that is a sign the install is being rule-of-thumb sized — and a poorly-sized heat pump is the single biggest source of post-install regret.

Application timeline and what to expect

Total from first call to commissioned heat pump: typically 4-6 months. Households who want a heat pump operational by next winter should start the process by late spring of the previous year.

Common reasons BUS applications get rejected

• EPC has outstanding insulation recommendations and the installer did not evidence why the recommendation should be set aside. The 2024 rule change makes this surmountable, but only if the installer documents it.
• Property is a new build under warranty — outside scope.
• Existing heating is not eligible — for example, the property already has a heat pump. BUS does not fund replacement of an existing heat pump.
• Heat pump model not on the MCS database at the time of voucher issue.
• Installer not MCS-certified for the specific technology (ASHP and GSHP are separate certifications).
• Voucher expired — the install was not commissioned within the validity window. Possible to apply for re-issue but not guaranteed.
• Heat capacity over 45 kWth — typically large rural properties. Out of scope.
• Hybrid system — gas back-up no longer eligible.

The single most common rejection reason in 2025 was the EPC insulation flag, despite the rule relaxation. Households can avoid it by asking the installer to confirm at quote stage that the EPC will not block the application.

What if my home is not heat-pump-ready

A heat pump produces heat at a lower flow temperature than a gas boiler — typically 35-50°C versus 65-75°C. This means the heat-emitting surface (radiators or underfloor) needs to be larger to deliver the same heat output.

For most UK homes, this means upsizing two to four radiators. For some homes — particularly small rooms with single radiators — it may mean adding underfloor heating or fan-assisted radiators.

If the heat loss calculation shows the home cannot be heated comfortably at any practical flow temperature, the installer should say so. Some homes need insulation work before they are heat-pump-ready. ECO4 or GBIS may fund that insulation if the household qualifies; otherwise the cost is on the household.

A good installer will discuss this honestly. A bad installer will install an oversized heat pump that cycles, runs hot, and produces high bills. This is the most common reason households end up unhappy with their heat pump.

BUS is one of the cleaner UK grant schemes — a flat voucher, a clear process, and a strong technical standard via MCS. The risks are commercial rather than regulatory: oversized systems, unnecessary buffer tanks, vague workmanship warranties. A well-prepared household with three competing quotes and a clear specification can usually get a comfortable, low-running-cost heat pump for £3,000 to £5,000 net.

For a quick eligibility check covering BUS, ECO4 and SEG together, run the Green Home Grants eligibility checker. If you would prefer an independent retrofit assessor to review your installer's heat loss calculation before you sign, the directory at Healthy Homes Network lists MCS and PAS 2035 assessors by region.