how do i fix my vokera linea 24?

how do i fix my vokera linea 24 it is not producing any hot water. All the parts have been checked (divertor, pump electronic circuit board) and are working correctly.
The pilot line continually goes on and off within 1/2 second and every time i turn the hot water tap on the temperature indictor drops from the 60 s to 15 degrees