David wrote:
So what is the real difference?
Can only some systems be run in reverse?
I suppose in simplistic terms it is like having a fridge which can also be
an oven, although my cool electric box can also be run as a warm box.

ASHPs in the UK are often targeted at wet heating systems (ie radiators).
It's not a good idea to run one of those in reverse because you'll get a
puddle of condensation under the radiator.

Air conditioning systems can often heat too, and I think that is heat pump
mode rather than a big resistor, but those are hot air systems.
You'd either need a big ventilation duct system, or need to have a unit in
every room to dispense air.

I don't know if there's something you can plumb an ASHP into that's like a
radiator but for cooling, which handles the condensation?

Theo