ASHP (Air source heat pump).

Together with downstairs underfloor heating and a multi fuel stove.
House is 7 years old, very well insulated. EPC (Energy performance certificate) is a B.
We had an ASHP in our last house. Very efficient. This one is somewhat more advanced.. the manual is the size of a full lever arch file.
There is a lot of misinformation going around about everyone should get an ASHP fitted. However they only work if the property is very well insulated to start with. And they are expensive to install if you are converting from another system.
Simply put the outside unit extracts heat from the outside air. It only takes around 1kW of electricity to power the pump to make around 3kW of heat.
Like a refrigerator in reverse.