Sorry on the delayed response. I'm in the US and sometimes have trouble getting into the UK side of the site.
Based on the symptoms you described, the most probable cause is a defective lamp power supply
, which is sometimes called the ballast.
The ballast's job is to "step up" or increase the 380V it receives from the power supply into a much larger kilovolt range level to light the lamp.
The part number on that is 934D054O50. I do not see any that are available here in the US, so you would have to search locally to determine availability and price. It will probably be expensive, I'm afraid. Either way, that would be the most probable cause and should be replaced at this point.
Hopefully that answers your question on why the unit is shutting down.
Perhaps unrelated but since I'm here, I thought you might like to know how to enter the service mode to determine how many hours are on each of the unit's assemblies, as well as their expected lifespan (in hours). Please >>click here<<
to download that chart.
Also, should the unit begin flashing some sort of code or sequence of colored LEDs, you can use this chart to help interpret them:
I hope that answers your question! If not, just let me know. Also, please take a second to rate the service I provided today, as that is the only way I receive credit for answering questions here. I hope I was excellent! Thanks!