Why has my pressure boosting water pump stopped working?

Model: DAB AUTO K-INOX 30/30 M
Installed: circa 2005

This boosts the water pressure in my 4th floor flat only.
The pump is installed high up on the 2nd floor of the building.
Input pressure is 3 bar.
Recently the pump became a bit slow to start sometimes necessitating opening the water taps to a greater extent than normal before the pump kicked in. Then the pump would occasionally stop working altogether for a period and then reset itself and start working again.
Now the pump has stopped altogether and the 'Alarm' light on the control panel is lit up.
When the 'Reset' button is held in for a few seconds the pump runs and the light goes out.
The pump now operates normally for a short time and then stops working and the 'Alarm' light comes on again.

Having read as much documentation on-line as I can find the symptoms seem to suggest the the pump is 'de-priming'. Is this possible while there is a constant 3 bar pressure on the pump's input and there is a moderate flow of water available at the taps even when the pump isn't running?
Is it possible that the pressure sensor is at fault?

Denis
December 2013