The towel rail feeds were on the wrong side of the pump and the way the pipework was done originally meant that there was a reversal of flow in one towel radiator when the circuits switched between HW & CH. There is what I think is a non-return valve where the CH pipe jons with the HW return...
I have a fully pumped central heating system - Potterton Sprima boiler 80L (about 4 years old), Grundfos Selectric pump, Honeywell Sundial Y Plan 3 position diverter valve, Potterton programmer.
I have had a number of problems with the system. The main problem is that when HW & CH are both on...