Two things decide whether a heat pump is a good idea, and both are already on your home’s certificate: what it burns today, and how well it holds heat. Enter a postcode.
A home on oil or LPG with no mains gas connection saves the most, and gets more grant. A home already on electric heating usually cannot claim the Boiler Upgrade Scheme at all.
Heat pumps run at lower flow temperatures than a boiler. In a home rated poor for walls or roof, that means longer run times and higher bills — insulation first is cheaper and it is the same work either way.
See what a heat pump costs nationally, or check a specific address for its own figure after grants.