Sophos UTM 9 Software Appliance seems to go down once or twice at the weekend.

Question

Good Day to you all, 
 We have an off-site UTM which manages my boss's home network and provides a back up to our office in case of emergency. 
 His wireless access, web filtering for machines, and other services are all provided to him through his firewall. 
 
 Over the last couple of months when the weekend comes around either the Friday or Saturday night at approx between 0040 and 0140, it will go down for no reason. 
 No access to WebAdmin page, no internet access, no logging, no nothing. This firewall is located in my Boss's top floor and hidden away in a back room. Everytime this happen he manually reboots the firewall and it continues merrily working away again until the next time it goes down. 
 
 What can I do? I'm at a loss here.... 
 
 Thank in advance..

RegencyBlue · Answer

Thought I'd update with what was wrong. Turned out to shutdown even when in Bios, my colleague noticed the processor fan was hanging off its connector and therefore the processor fan was not always working when it should have been. 
 
 Re-applied some thermal paste and ran the memtest which it passed with flying colours. Hasn't gone down since! Those temp errors have stopped too.