Thanks for the help! The fan runs on high for around 10-30 seconds (plus the red lights) and then goes quiet, but does this continuously every so often. So I assume the fan does work.
Already tried rebooting and have tried quitting iCue. Neither changed anything. I have now tried changing the fan profile as it was set on default. On a 50% profile then fan doesn't kick in and temperatures seem fairly stable. It's a good workaround as Extreme is way too loud. However, just 2 days ago it was on default and was working fine. At least for now, 50% allows me to continue to use the PC but I would feel better knowing if this is normal or something inside is defective resulting in having to use a higher fan profile, even on low load.