Update:
Unfortunately my Z5 has done it again.
The error code I'm getting when it switches off is a flashing red power light and a flashing amber replace lamp light. According to the manual it means the lamp is on its way out. The weird thing is if I turn if off at the mains and switch it back on it usually fires up ok and I haven't noticed any problems with the brightness etc.
I'm going to give Ivojo a call later today for some suggestions so fingers crossed. If it does turn out to be the lamp after only 147 hours I think Sanyo will make it on to my bad brands list!
Cheers,