Heat pump or gas boiler when your boiler fails: what to choose

What to know first

This summary covers the immediate choice, installation work, costs and funding after a boiler breakdown.

Practical interpretation: the direct answer depends first on time. A gas-boiler repair or replacement may be easier where heat must return quickly because a heat pump needs assessment and design. A heat pump becomes more realistic where temporary heating is manageable, there is time for a proper design, and the household accepts any required alterations.

This article focuses on a standard air-to-water heat pump compared with a replacement gas boiler.

Heat pump or boiler: the quickest way to decide

This table is a starting point, not a technical assessment. Gas work requires a Gas Safe registered engineer. An MCS-certified installer should assess and design a heat pump funded through the Boiler Upgrade Scheme.

Editorial interpretation: because an MCS-compliant heat pump needs assessment and detailed design, it is less likely to be an immediate like-for-like replacement than a straightforward boiler change. Timings still depend on the property and local installers.

How much time do you have?

Energy Saving Trust says the wait for a heat pump can be several months. Fitting typically takes about three days, but radiator, pipework or building work can extend it. Heating is normally off for much of the installation.

Ask how rooms and hot water will be covered, what temporary equipment is included and what happens if the schedule slips. Portable electric heaters may help with rooms, but they do not provide a complete heating and hot-water replacement.

Expert insight

“Treat the breakdown and the replacement as separate problems. Temporary heating can create time to compare long-term options properly.”

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

What changes might a heat pump need?

A heat pump should be designed around the home’s heat loss: the heat escaping through its fabric and ventilation on a cold day. MCS requires room-by-room calculations and written details covering room heat losses, heat-emitter sizes, hot-water demand and estimated performance.

Radiators, pipework and flow temperature

“Flow temperature” is the temperature of water sent around the heating system. Heat pumps generally work most efficiently at lower temperatures than boilers, so some radiators may need to be larger. Pipework and controls can also need changes.

If a design proposes more than 55°C, MCS says the customer should also receive an alternative at 55°C or below, with the efficiency and energy-use differences explained. This does not mean every radiator must be replaced. The room-by-room design should show what is needed.

Hot water and space

A standard air-to-water heat pump normally heats water stored in a cylinder rather than providing it on demand like a combi boiler. Energy Saving Trust says a cylinder can often fit in a cupboard with roughly 80cm by 80cm of floor space, although the correct size depends on hot-water demand.

An existing cylinder is not automatically suitable. Its size, heat exchanger, insulation and reheat time must fit the proposed design.

Good to know — think beyond today’s replacement

Choosing a combi boiler now removes the cylinder, but most heat pumps need one. A later conversion could therefore mean putting hot-water storage back.

Outdoor unit, electricity and permissions

The outdoor unit needs airflow and a position that meets noise and planning requirements. In England, many installations are permitted development only if all conditions are met. From 28 May 2026, the relevant standard is MCS 020a. Rules differ across the UK, and flats, listed buildings, conservation areas and leasehold homes need particular care.

The installer must notify the distribution network operator, which runs the local electricity network, and seek advance permission where required. Any electrical upgrade should be identified before the contract is finalised.

How do the upfront and running costs compare?

A replacement gas boiler normally has the lower headline price. Energy Saving Trust estimates an average £3,500 in Great Britain for replacing a G-rated gas boiler with an A-rated model and thermostatic radiator valves. Its July 2026 typical figure for an air source heat pump is about £12,000, with property size and radiator work affecting the quote.

Ofgem’s 2025–26 scheme report recorded an average total air source heat-pump quote of £13,441 before the grant was deducted. This included the system, labour and VAT where applicable. Ofgem did not validate the submitted figures and excluded the highest and lowest 10%, so this is not a fixed market price.

Compare complete quotations. A heat-pump quote should identify radiators, cylinder, pipework, electrics, controls and making good. A boiler quote should cover the boiler type, controls, cleaning, filter, flue work and warranty.

Running costs are not certain. From 1 July to 30 September 2026, Ofgem’s average Direct Debit cap rates were 26.11p/kWh for electricity and 7.33p/kWh for gas, including VAT. Heat pumps use electricity efficiently, but performance varies. Energy Saving Trust says standard-tariff running costs can be slightly higher than for a new gas boiler, while a suitable time-of-use tariff can change the result.

Expert insight

“Do not compare fuel prices alone. Compare estimated annual use, tariffs, standing charges and the property’s heat-pump performance estimate.”

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

What funding could change the calculation?

In England and Wales, the Boiler Upgrade Scheme is an upfront discount through the installer. Checked on 21 August 2026, the standard air-to-water grant is £7,500. Eligible off-gas-grid homes replacing oil or liquefied petroleum gas can receive £9,000 for applications properly made from 21 July 2026 to 31 March 2027. Ofgem decides eligibility after an installer applies; it does not offer pre-approval.

The quote must show the price before the grant, the grant and the balance. Check what the contract says if an application is rejected or a voucher is revoked, because liability for the discount depends on the agreed terms.

Scotland’s separate Home Energy Scotland scheme offers eligible owner-occupiers up to £7,500 as a heat-pump grant and an optional interest-free loan of up to £7,500. A £1,500 rural uplift can apply. Funding is limited and work must not start before a written offer.

In Wales, BUS can apply, while Nest may fund a heat pump for qualifying households. Northern Ireland has different arrangements; NI Energy Advice provides impartial advice and referrals.

Qualifying supplied-and-installed energy-saving materials, including fixed air source heat pumps, are zero-rated for VAT until 31 March 2027. A 5% rate is scheduled from 1 April 2027. Separate building work can be taxed differently, so check the itemised quote.

A safer way to make the decision

1. Diagnose the failed boiler. Use a Gas Safe registered engineer for gas or LPG work, and ask whether repair is safe and economical.

2. Plan temporary heat and hot water. Confirm the equipment, expected cost and workable duration.

3. Price both routes. Obtain itemised boiler quotes and, where time allows, quotes from at least three MCS-certified heat-pump installers.

4. Compare the whole job. Include radiators, cylinder, pipework, electrics, permissions, making good, warranty and aftercare.

5. Check funding before work starts. Apparent eligibility is not approval.

6. Read the contract. Confirm dates, deposit arrangements, cancellation rights, grant risk and responsibility for extra work.

An MCS-certified installer should make the final heat-pump design assessment. A planning authority, freeholder or managing agent may need to confirm permissions. The installer normally handles electricity-network notification, but the contract should allocate responsibility for any resulting work.

Key takeaways

• A boiler repair or replacement is usually simpler where heat must return quickly.

• A heat pump is more realistic when there is time for design and home alterations.

• Cylinder space, radiator sizing, outdoor siting and electrics can affect suitability.

• Heat-pump installation normally costs more upfront, although grants may narrow the gap.

• Lower bills are not guaranteed; design, controls and tariff matter.

• Funding, VAT, prices and lead times were checked on 21 August 2026.

Frequently asked questions