Both upgrades cut carbon and both cut bills, but they solve different problems and their economics are not the same.
The short answer
If your gas boiler is under about ten years old and working fine, solar first. It is cheaper, quicker to install, needs no changes inside the house, and starts saving from day one.
If your boiler is at end of life, heat pump first — because the £7,500 Boiler Upgrade Scheme grant only applies to the heat pump, and you would otherwise spend £3,000 on a replacement boiler you will remove later.
Side by side
| Solar PV | Air source heat pump | |
|---|---|---|
| Typical net cost | £6,000 - £8,500 | £2,000 - £7,000 after grant |
| Install time | 1-2 days | 2-5 days |
| Grant | Zero VAT | £7,500 Boiler Upgrade Scheme |
| Disruption | Roof only | Cylinder, pipework, some radiators |
Where they overlap
Solar generation peaks in summer; heating demand peaks in winter. So solar will not cover your heat pump running costs — it typically offsets a modest share across the year. The pairing that genuinely helps is solar plus a battery on a time-of-use tariff, charging cheaply overnight.
What to do next
Get quotes for both. Seeing the two numbers against your actual roof and heat loss makes the decision obvious far faster than any general guide can.