Hot water but no or little flow in radiators

[sthergk]

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 the rads do not get warm, even after several hours. When I switch to CH only the rads get a little warm at the top but it seems to take a long time. The return pipe back to the boiler appears to be cold still after several hours. Is this a problem with sludge in the CH system or a faulty 3P valve? There are two towel rails fed before the 3P valve which I have turned off to try and increase the flow in the CH, but the boiler then locks out.
There is still a lot of air in the system even after 4 weeks of refilling it after I moved the pump. After moving the pump the system worked very well for a week or so and then went back to its same problems.

 

[namsag]

So why did you move the pump.
Divertor valve? does it have 3 or 5 wires
4 year old are you sure you don`t have a heat store cylinder if you do hot water has to be on constantly and up to temp before it will turn on to heating

 

[sthergk]

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.
There are 5 wires coming in to the programmer from the diverter valve.
I have an insulated hot water storgae cylinder and this has a thermostat on the side of it