How do you test a circulation pump on a Raven Heat Combi boiler?

Ive got a Ravenheat Combi Boiler (one without a pilot light window). A fw weeks ago it just stopped working. When switching to on you do hear the usual click but nothing happens, no whirring or anything else even when the hot water tap is opened fully for several minutes or when the c/h temp is turned right up. Electricity is fine but i cant get the cover off the unit to check the status of the pilot light as the builder has plastered right around the thing. What signs can i look for to see whether the circulation pump or pump valve is the cause? If the pump is OK shoudl the boiler make a whirring noise when it is witched on (it doenst at the moment). There is sufficient water pressure in the heating system and theres been no change in cold water in/feed pressure.