Thank you all. I move it around and couldn't get any readings - it was stuck at 8 degrees.
Fiddled with the connector since it seems quite flimsy, but no joy. In the end, switching the the alternate cable solved it, so there must be a weakness somewhere else along the cable. I pushed the heat-shrinked black tube through a bit more to ease stress and for now I've got it working, so I'm happy.
Thanks again
- Roo