I didn't know about the temp reading. With the cover off, the temp was 24 to 26 degrees. With the cover back on (loosely covering 80% of the box) the temperature increased to 34 degrees and after 30 mins the box rebooted. I decided to force the issue and put the cover back on fully, covered the vents on the top of the case and turned the fan off. The temperature rose quickly to 42 degrees and the reboots increased to a point where they were happening every few seconds and I didn't have time to access the temperature menu item to see what the max temp was but it looked like conclusive evidence of heat-related problem. I put the fan on full power and uncovered the vents and the occurrences of the reboots began to reduce over a few minutes - although I had to switch the box off a couple of times as it was stuck at the 'Starting' point. Also, at times it took longer than usual to go through the boot-up process. Eventually, the temperature stabilised at 26/27 degrees and the box was usable again but I got a couple of reboots at this temperature which is annoying and contradicts the earlier conclusion. I left the box off overnight and this morning it is running at 20 degrees and no reboots after an hour - fan on full, cover on and everything else is installed/running. I'll post an update tonight.