Heating Fault - Pump continually runs (Maxol microturbo 402)?

I have a Maxol microturbo 402 domestic boiler that is used for the central heating and hot water in my home. The system appears to have developed a fault whereby the water pump in the system continually runs . . . even though the programmer is set to off. I understand that when the boiler turns off the pump keeps running in order to remove the heated water from the boiler. However; my pump keeps running indefinatey!! The only way I can get the pump to stop running is to turn the power off to the pump (by turning off the power to the programmer box, pump and electrical valves).

I have tested the electricaly operated valves on the central heating and the hot water. Both of these seem to operate ok and open and close if correctly depending upon the demand from the programmer and the thermostats.

I now think that the most likely cause of the fault is the over-run switch in the boiler (I'm assuming there is one but can't be sure as the previous owner has not left any of the manuals!!!) Is there a way that I can test to see if the over run switch is operating?

Also are there likely to be any other faults which could cause the same symtoms? Anything to do with the microswitches in the electrically operated valves maybe???

Any help would be appreciated,

Simon