Baxi Solo 70/4 failure?

On Xmas eve boiler main or pilot solenoid started loud clicking/knocking with main burner flashing on/off voilently no matter what temperature setting on boiler. When shut down and restarted when hot or cooled down, the pilot and burner light up quickly and normally for about a minute then the loud valve clicking/knocking starts. I assume the solenoids valves are ok and that the problem is with the signal feeding them. What could be causing this? Is it most likely the control box/control sequencer? Will a new PBC solve the problem? The first two orange indicator lights stay on and the third one flashes in line with the cliking/knocking of the valve. Needless to say, without heating the house is cold, no help avialable at present so would welcome any advise as to what problem could be and if I can do anything in the meantime. Thanks for any help