Thank you Charnwood. Qui docet discit - great quote - every time I prepare lessons, it is a learning experience.
JohnD, many thanks to you too.
GavThePlumber, the problem I was having (and I am not sure yet whether it has been solved - I'll turn on the heating later this evening and monitor what happens) was this. As expected, all the rads would heat up as the target temperature on the room stat was being achieved by the boiler but, because there is a TRV in the same room (hall) as the room stat, the boiler would shut off when the TRV temperature was reached. Therefore, the other rooms would begin to cool down to discomfort levels.
Two nights ago, I lowered the TRV in the hall and noticed that the room stat could not reach its target temperature of 18 degrees (stopping at 17.5) This was the first evidence I had that convinced me that there was a conflict. Yesterday evening, after searching for answers on the Internet, I removed the TRV head completely. I have had this issue for two years (since my new heating system was installed). Next step is to reduce the LS valve opening. If this doesn't work, but I don't see why it shouldn't, I'll lower the LS valve setting further.