I have a small bore central heating ,and you do need to balance the system lots of people have all the valves wide open,which will slow the flow around the house,best to work out which rads are fed first and shut them down a bit also any small rooms do the same ,it may be that you have some sludge in the system,maybe when it gets warmer you could drain the whole system and refill,with regard the Nova Setter I do not have one but would suggest putting it on B and try that if this fails to cure problem then try F.