Getting Hot Water, But No Central Heating (combi boiler)?

Are you sure it is the pump running and not the fan that you can hear? Onthe 100e the fan doesn't run all the time, only on demand. Switch of the juice and take the front off the boiler(2 screws at the bottom). Try venting the pump through the vent screw. It might be that the divertor valve is stuck in the hot water position so the boiler is firing with nowhere for the water to go