I have a vented central heating system with 15 radiators. I have had to balance the system with the radiators nearest to the boiler and pump almost locked off completly to ensure that flow reaches the furthest radiator. The problem now is that even though the radiators do get hot (eventually) the return flow is always luke warm therefore the bolier is always fired up heating the water.
If the boiler is purely heating the hot water tank the boiler operated as expected. Fireing every 5 / 10 mins or so.
I have powerflushed the system and that has not helped
New Pump - If so what size? 15/50 or 15/60
Still not balanced properly? - If so how can I ensure flow gets to the end radiator - Furtherest radiator is about 12metres away from pump