Baxi Combi 105 HE condenser boiler pump question?

Can any one point me in the right direction with regards to the pump operation after the CH shuts down after boiler reaches the room stat temp.
My boliers pump constantly runs after the boiler has shut down when it reaches the stats temp. I understand that the pump will shut down after a few mins, but my pump still runs until the boiler fires up again.
The pump works 100% on the HW side.
So is this problem the CH temp sensor or on the PCB. The boiler worked fine until the CH differential valve valve stuck. The diaphragm was changed , and the problem of low system pressure/ fault on pump was cured.
Any advice would be appreciated.