My Boiler Is Old: Should I Replace It with a Heat Pump?

Your boiler is playing up, or it has failed entirely. You have three options in front of you, and the right one depends on your circumstances, your budget, and how long you plan to stay in your home. Here are the honest numbers for each, so you can choose under pressure.

Your Three Options

Option 1: Repair the Existing Boiler

If your boiler is repairable and not too old, a repair buys time. On our estimates a repair costs anywhere from £100 to £900 depending on the fault: a sensor, valve or fan is typically £200 to £450, and a PCB or heat exchanger £400 to £900. British Gas charges £295 for a one-off fixed-price repair, with exclusions where separate work is needed. How long a repaired boiler keeps going depends on its age and what failed; on an old boiler, we'd treat it as buying a year or two, not a decade.

This makes sense if: you are mid-way through a major renovation and want to delay the decision, or if your home is not yet ready for a heat pump (poor insulation, very small outdoor space) and you need time to prepare.

It does not make sense if: the boiler is over 15 years old and has already had multiple repairs, or you are paying very high gas bills and want to start saving now.

Option 2: New Gas Boiler

A new condensing gas boiler costs around £2,750 installed on our estimate, and lasts 10 to 15 years. It is a known quantity: a like-for-like swap is a familiar job for any heating engineer, and it's compatible with your existing radiators and hot water cylinder.

The case for a new gas boiler is weakening. The government's Warm Homes Plan targets over 450,000 heat pump installations a year by 2030, so that's where government money is pointing. You could still claim the BUS grant later, when that new boiler reaches the end of its life, because you'd still be replacing fossil fuel heating. But you'd have paid for a boiler you then take out, and nobody can promise the grant will be there in ten or fifteen years.

A new boiler still makes sense if: you have a very small outdoor space with no viable location for a heat pump unit, your home is listed (a heat pump on a listed building isn't permitted development, so you'd need consent), or your home is so poorly insulated that a heat pump would be impractical and expensive to run until major works are done.

Option 3: Heat Pump

A heat pump costs about £11,100 to £15,600 installed before any grants. That's the middle half of real installs in April to June 2026 in the DESNZ Boiler Upgrade Scheme statistics, with a median of £12,908. A typical 3-bed's 6 to 8kW unit came in at a median of about £12,200, and that's the figure the sums below use. If your semi already has filled cavity walls and a full loft, our heat loss model puts it nearer 5kW, where the median was about £11,500: that's what the checker above shows. The Energy Saving Trust puts the typical figure at around £12,000. The £7,500 Boiler Upgrade Scheme (BUS) grant brings the middle half of installs down to about £3,600 to £8,100, so typically £900 to £5,400 more than a new gas boiler, not ten thousand more.

The BUS grant is applied by your installer: they deduct it from your invoice and claim it from Ofgem. You never handle the grant money directly. The key eligibility requirements are that the property is in England or Wales and you own it, you're replacing a fossil fuel heating system, and your installer is MCS-certified. You don't need an EPC and you don't need to clear insulation recommendations first; both conditions have been removed.

10-Year Cost Comparison

The table below shows total expected spend over ten years for a three-bed semi currently paying around £1,500 a year for gas heating. That's our example of a bigger or draughtier 3-bed than our typical £950 to £1,000, because the case for a heat pump is stronger the more gas you burn. Here's where that number goes: take off the £108 gas standing charge and you're buying £1,392 of gas units, which at 7.97p/kWh is 17,500 kWh of gas. At 90% boiler efficiency that's 15,700 kWh of heat in the house. A heat pump at SCOP 3.0 needs 5,240 kWh of electricity to deliver the same heat, and at 26.32p/kWh that's £1,380 a year. Each row then adds a yearly service at British Gas's one-off prices: £119 for a boiler and £189 for a heat pump.

At SCOP 3.0 a heat pump is roughly level with gas on running cost. With the service, £1,569 against £1,619 is a £50 a year difference, and over ten years the grant-funded heat pump lands at £20,390 against the boiler's £18,940: £1,450 apart, the boiler's way. Anyone telling you the running cost alone makes this decision is not doing the sum.

What actually makes the case is the two rows below it. Push the SCOP from 3.0 to 3.5, which is what we'd expect a properly designed system on correctly sized radiators to manage, and you're £550 ahead of the boiler. Add a heat pump tariff on top (Cosy Octopus, blended to roughly 20p once the day-rate hours are counted, our estimate) and you're £3,350 ahead. The £7,500 grant plus a heat pump tariff is the argument. The fuel switch on its own isn't.

Two things to know about the table. It counts the £108 gas standing charge on the boiler rows and not on the heat pump rows, so it assumes you have the gas supply disconnected; keep the gas for a hob and add about £1,080 over ten years to each heat pump row. And the repair row is flattering: a repair buys you time, not ten years, so realistically you're back at this table again with a dead boiler.

Model your own numbers with our heat pump savings calculator. The heat pump also lasts longer, typically 15 to 20 years, and some well beyond that with servicing, against 10 to 15 for a gas boiler, which pushes the longer-term picture further its way.

Step-by-Step: How to Replace Your Boiler With a Heat Pump

Step 1: Check You're Eligible (No EPC Needed)

You do not need an Energy Performance Certificate to apply for the BUS grant. That requirement was removed on 28 April 2026; the separate "clear your outstanding insulation recommendations first" condition had already gone on 8 May 2024. gov.uk's eligibility page now asks only two things: that you own the property, and that you are replacing a fossil fuel heating system (England and Wales only). It says in terms that you're still eligible if you've already had funding to insulate. If a site tells you to buy an EPC first, it is out of date. Insulating first is still worth doing, because it lets your installer specify a smaller and cheaper heat pump.

Step 2: Get a Heat Loss Survey With Each Quote

A heat loss survey is a room-by-room assessment of how much heat your home loses on the coldest design day. It determines the correct heat pump size and identifies which radiators need upgrading. Each quoting installer should do one as part of quoting (some charge for it). We wouldn't pay for a separate one beforehand, and we'd never accept a quote from an installer who hasn't done one.

Step 3: Get Three MCS Installer Quotes

Your installer must be certified by the Microgeneration Certification Scheme (MCS) for you to receive the BUS grant. You can find certified installers on the MCS website. We'd get at least three quotes: prices for real installs vary by about £4,500 across the typical range (DESNZ). Make sure each quote includes the heat loss calculation, a system design, and specifies which radiators (if any) need replacing.

Step 4: Apply for the BUS Grant

You don't apply directly. Your MCS installer submits the application to Ofgem, normally before installation begins. You then confirm to Ofgem, within 14 calendar days, that you've agreed to it. Ofgem then says your "installer has three months from the moment the application is approved to complete the installation ... (six months for ground source heat pumps)", which matches regulation 15(2) of the BUS Regulations 2022. And if the system has already gone in, it isn't necessarily lost: Ofgem accepts applications for a system commissioned up to 120 days before the application is properly made. The grant is deducted from your invoice.

Step 5: Installation

Expect a few days to a week: British Gas says most of its heat pump installations take five days, and Octopus says most of its installs take a few days. The outdoor unit is fitted and connected to your internal pipework, and a hot water cylinder goes in if you don't have a suitable one. Controls and thermostats are installed (see our best smart thermostats for heat pumps), and the system is commissioned and tested. Octopus says hot water is usually back on by the end of the first day.

Timeline: From Decision to Running

If your boiler has failed and you need heat urgently, discuss interim solutions with your installer; some will provide temporary electric heaters during the wait. And remember the 120-day rule: if you genuinely can't wait, the installer can fit the heat pump first and apply within 120 days of commissioning, though applying first is safer.

The Bottom Line

If your boiler has failed and you can get the £7,500 grant, a heat pump is the right call, but probably not for the reason you'd expect. At SCOP 3.0 you're level with gas on running cost, within about £50 a year with servicing, and the ten-year totals land £1,450 apart in the boiler's favour. That's not a saving you'd plan your finances around.

What makes it work is the grant bringing the net install cost to within about £2,000 of a new boiler, and a heat pump tariff turning a level running cost into a genuinely cheaper one. Get the grant, the tariff and a good design (45C or lower) and that home is £3,350 better off over ten years than fitting another combi. Without the grant, it'd have been better off with the boiler. Get the grant but accept a sloppy 55C design that lands at, say, SCOP 2.5 (our illustration), and you've spent the grant to make your bills worse.

So the practical advice is narrow: take the grant while it's there, insist on a design flow temperature of 45C or lower with a predicted SCOP in writing, and move to a heat pump tariff on day one. If your installer can't or won't do the first two, a new gas boiler is the honest answer for your house.

The key question is whether your home is ready. See our guide to heat pumps in old houses if your property was built before 1980, or our radiator upgrade guide to understand whether your existing radiators will work. For a full cost breakdown, visit our heat pump costs guide.