Quote Originally Posted by pauby View Post
Which is more likely?

How do I sort it, assuming it's the air path being blocked (I assume by ice)? Would my suggestion of pouring boiling water into each channel in turn make matters worse?

Yes, leave it off (unplug it from power supply) for at least 48 hours and then check again. That should be enough for thaw ice if that is the case.
If that doesn't help you need to reach fan by dismantling his enclosure.