just wondering, how are they coping in in this weather? I'm all for change but I can't be doing with a lukewarm shower.

I don't have one myself but my father does. His system is working perfectly and has done for five years now.
He's in the Highlands so he sees his fair share of freezing temperatures, not once has he encountered any problems. As I live just a few miles away from him, I know he has had temperatures as low as -19C in winter. His home has remained at 21C (his choice) throughout each winter.
The system he has is supposed to work as expected down to -15C but it's been colder than that on several occasions and the system still works.
I hope that helps.

Have wondered this, thanks for the info Sonic.

They seem pretty ingenious things, staggers me how well they seem to work.

Do you know what type it is, looking myself. Air or ground sourced? Thanks