For those interested in installing heatpumps I can describe my experience in running a rather big one that provide sanitary hot water for 6 holiday apartment we own and one for AC/heating for each of said apartments.

In summary, switching to heatpumps was a win. In fact, the sum of monthly bills went down by around 30% compared to having electricity and gas. In addtion, they don't require the yearly safety check-ups and smoke tests that gas boilers of that size did. The downside is that you have to do small maintenance more often since there are more moving parts that fail.

We have been running them since 2017, so I only have data for 6 years (5 if you don't count 2020 which for tourism was a bloodbath). The maintenance frequency is not going up, but the costs went a bit up in 2022 due to more expensive parts. If things stay this way we would break even in an additional 2/3 years, granted that we had to do quite a big renovation and so my cost figures of when we did the works are not perfectly attributed. The company that installed the units says they have a lifetime of 15/20 years, and so well worth them as by them we would have saved enough to update the heatpumps with money to spare.