Weather compensation is the one that matters. An outdoor sensor tells the boiler or heat pump how cold it is outside, and the flow temperature moves to suit — 40 degrees on a mild October morning instead of the 70 it would otherwise send out and then cycle off. It means the heat goes in gently and steadily instead of in bursts, the house stays at a flatter temperature, and a condensing boiler actually condenses, which is the entire reason it is called one. Most condensing boilers in this country never condense properly because they are run at a flow temperature that makes it impossible.
Zoning is the other half. A single thermostat in the hall is measuring the coldest, draughtiest, least-used room in the house and using it to decide the temperature of your bedroom. That is how most houses are wired. Splitting into real zones — upstairs and downstairs at a minimum, and room by room where there is underfloor — means each part of the house gets what it needs.
The bit we will talk you out of: smart TRVs on every radiator in a house that has never been balanced. They will fight the boiler, they will close down enough of the system that the flow has nowhere to go, and you will have spent several hundred pounds to make things worse. Balancing the system costs less and does more. If you want smart TRVs after that, fine — but in that order.
On a heat pump, controls are not optional decoration. The whole efficiency case rests on running the lowest flow temperature that will hold the house, which is exactly what weather compensation exists to do. A heat pump on a fixed 55 degree flow with an on-off thermostat is a heat pump running like a bad boiler.
