BOILER OVERHEAT-NO CH BUT HAVE HOT WATER

I have a Baxi Solo 2 60PF boiler (about 5 yrs old) everytime I try to put the Central Heating on the overheat light comes on within 20 mins . Even when it doesn't the radiators don't get warm. If i just heat the hot water i get hot water fine. HELP.
Cheers,
J

Poor circulation. Dying pump??? Is it on max speed?

Pump is on maximum speed...Don't know any reason why circulation would be poor.

The pump can be on max speed but is it spinning ?
If it is spinning are you sure the impeller is still attached to the spinning shaft?
Is the pump dragging sludge around the system?

Having said that it sounds like a pump over run problem. I would be checking to make sure that the pump over run is working after the boiler has finished its cycle.
Assuming there is no over run, check that the pump is correctly wired into the boiler so that the pump over run can work properly. After that the temp sensor and pcb are suspect.