i would politely suggest that people stop commenting/assisting this poster and let them deal directly with the installer, who should address the issues that are apparently occuring.....from install in the past couple of weeks...or is their something else.....
if you are that concerned get the installer to address/answer your questions rather than random strangers who have no idea of sys/size/req/preferences or location of equipment...a two bed flat would heat quicker than a three bed semi subject to various factors/preferences.
you should know better,than to ask these questions after all its the plumbers fault the previous rad worked perfectly for the last 10yrs and was only changed because they wanted a different rad with a higher output in a different position.......
boiler has reached set temp internally and needs to loose some heat before refiring turning it off does not help the heat,sounds like it is a circulation/dirt issue and external issue,turn it on and leave it run for a couple of hours on 3 or 4 on the stat/dial.
edit. make sure all valves are...