This is funny timing. I have an ASHP (14kw Ecodan) that’s been in this house for ten years. And tomorrow it’s getting removed and replaced with, whisper it, oil combi boiler (as was in before the ASHP). It has been repaired a couple of times now (compressor repairs, re-gassed etc) and is now just not worth spending any more cash on. It feels like a HUGE backward step but the truth of the matter is that in a house that isn’t either designed for it, or subject to major work in terms of the introduction of appropriate insulation, it’s just not economical (nor comfortable even with an Aga and a big wood burning stove).
My old house which we completely renovated from just 4 walls was heated by a 7kw ASHP (another Ecodan) and it was absolutely fantastic. But we spent thousands and thousands on insulation to give us the best chance.
In summary though, and in my experience, (and the right energy tarrif – we were on E7 as thats when the Aga took its power too), they’re a great technology if somewhat limited by the current limitations of building regs relating to insulation and appropriate design of new build homes.