Thinking about heat pumps, since there's been waffle on the radio about them recently. My mental model of a heat pump is that you have unit(s) outside, and aircon unit(s) indoors which you can run either to cool or heat your preferred rooms.

However, what's being talked about on the radio seems to consist of hooking a heat pump up to replace your gas boiler and warm your radiators. Is this more effective or efficient? It seems to me that as the chances of hot weather increase you'll want to cool your house for some of the year, and this doesn't do that.