Had an RAC man out for a problem on my A6 this morning and he kindly plugged his fault code reader into my A3 as well to see if there were any codes showing. It was showing the following:

17056
17057
17058

All of which were for Electrical Fault Intermittent - Glow Plugs (2,3 and 4).

Can anyone clue me in on what this means and whether I should be doing anything about it? He also said it could have been an old problem that was rectified and didn't have the faults cleared. Is there an obvious way to tell whether the faults are valid or not?