Just messed around with it again. And I found out the constant hot water issue. It was the salmonella prevention system that always heats up the boiler to kill the bateria. Because I was always turning the thermostat off it restarted again the procedure.
Problem solved.
Cheers for your help...
I have dismantled it and replaced it with my the old thermostat, however, I have followed the below diagram and ended up with the same Heat Link as per picture.
I also have a system boiler, with a water tank if it makes a difference.
Thanks
I have been spending a lot of time at home (due to the coronavirus epidemic), and I decided to take the plunge, learn something new and replaced my Danfoss TP9000 with a nest thermostat 3rd generation.
After reading a lot of forum and posts online I was pretty confident that it would be easy...