HID headlamp problem

[matchmaker]

My Octavia has factory fitted HID headlights. The original bulbs only lasted 150,000 miles until I had to replace them. Since changing them one has occasionally failed to "strike". Switching them off and on again sorts this. I changed the offending bulb but still have the same problem, so suspect the problem is something else. What is it likely to be - ballast?

[p4cks]

It does sound like the ballast.

Also, when removing and refitting the headlight bulb remember to wear gloves so you get absolutely zero skin to bulb contact