Heat pump or solar panels: which should you install first?

Quick answer: If your gas boiler is near the end of its life, heat pump first. The £7,500 grant cuts our modelled £11,014 install to £3,514, and a failing boiler would cost around £2,804 to replace anyway. If the boiler is young and healthy, fit solar first at £6,496 and let it earn while you wait.

Plenty of homeowners plan to do both eventually. The order matters more than most guides admit, and it turns on one question: how much life is left in your boiler?

The two projects side by side

Cost figures are our modelled estimates for an average UK three-bed; the method is on our how we calculate costs page. The solar benefit assumes a system generating around 3,400kWh a year in average UK conditions (Sunsave, checked July 2026), with roughly half used at the 26.32p cap rate and half exported at a mid-range Smart Export Guarantee price. Your tariff moves that number, so treat it as an estimate. We haven’t tested any of this hardware; the figures are modelled estimates and published data, checked July 2026, with the October–December 2026 cap rates checked September 2026.

Why the boiler decides the order

Here’s the maths people skip. At the October–December 2026 cap, a heat pump with a SCOP of 3.5 makes heat for about 7.5p/kWh. A 90% gas boiler makes it for about 8.9p (Ofgem cap rates). So the heat pump is now about 15% cheaper per unit of heat. On Ofgem’s typical 9,500kWh of gas a year, that saves about £114, or about £223 if you give up gas entirely and stop paying its standing charge. Worth having, but it would take 16 to 31 years to earn back the £3,514 of replacing a boiler that still works.

Now run it with a dying boiler. You were about to spend £2,804 on a replacement, on our modelled figure. The heat pump costs £3,514 after the grant. So the true premium for going electric is £710, and £114 to £223 a year in lower running costs pays that back in three to six years. That’s the cheapest route into a heat pump anyone will ever offer you, and it’s why boiler failure is the moment to move.

A young boiler flips it. Scrapping eight years of remaining service throws money away, while solar starts earning the day the scaffolding comes down and doesn’t care what heats your radiators.

Two cap rates also sit quietly behind this. Gas at 7.97p is historically cheap against electricity at 26.32p; the ratio is about 3.3 to one. If future caps narrow that ratio, the heat pump’s running-cost case improves and the order tilts further its way. We track the moving parts on our statistics page.

The sequencing effect

There’s a second reason to put the heat pump ahead of solar when both are close: a heat pump turns your home into a much bigger electricity user. Size the solar array afterwards and your installer designs around real demand rather than guesswork.

One honest caveat. Solar won’t run your heat pump through winter. Generation peaks in June; heat demand peaks in January, when a UK array produces a small fraction of its summer output. The pairing still works across the whole year, through export income and shoulder-season hot water, and a battery stretches it further. Our heat pump and solar combination guide goes deeper, and battery storage has its own numbers.

Where insulation fits in the queue

Strictly this is a two-horse question, but a third contender belongs in it. Our modelled cost for loft insulation is £1,498, a fraction of either project, and it shrinks the heat pump you eventually need. A smaller heat pump costs less to buy, and a well-insulated home lets it run at lower flow temperatures, which is where the efficiency lives.

So the real order for most homes is: cheap insulation first, then the boiler-or-solar decision above. Bolting a heat pump onto a leaky house is how the horror stories start. The options are in our insulation guide.

Three situations, three answers

Boiler over ten years old, or already misbehaving: heat pump now, solar after. The grant does the heavy lifting and the timing costs you nothing.

Boiler under eight and reliable: solar first. Revisit the heat pump when the boiler declines; the Boiler Upgrade Scheme runs to March 2030, so there’s no scramble.

Doing both within a year: heat pump first, solar second, sized to the new load. Separate trades, separate scaffolding, no clash. And if roof repairs are already planned, fold the solar into them; shared scaffolding is free money.

Whatever the order, both purchases sit at 0% VAT until 31 March 2027, and our calculator prices each for your home. If you’re still weighing either technology up, start with the heat pump guide and the solar panel guide.

FAQs

Can I claim the grant and still add solar later?

Yes. The £7,500 Boiler Upgrade Scheme applies to the heat pump only and has no bearing on solar. Both benefit from 0% VAT until 31 March 2027 (gov.uk).

Will my solar panels power the heat pump?

In summer, comfortably, when the heat pump has little to do. In January, barely. Treat them as two investments that share a meter rather than a closed loop.

Should I wait for heat pump prices to fall?

Waiting has a price too: every winter on a failing boiler risks a distress purchase, and a rushed like-for-like boiler swap locks in another 10 to 15 years of gas. If the boiler is fine, waiting costs little: the heat pump would save £114 to £223 a year, against £3,514 to switch. That’s the solar-first case in one sentence.