Thanks, Cor.
Yes everything seems OK with the Universal sensor, it's just two out of the four temperature sensors that make no sense. I mean, if they read 0C I could probably understand it, but they don't. It's these two specific sensors (even if I put one in my conveniently placed freezer, it continues to insist that the temperature is 20.25C)
Very odd, given all the sensors are using the same single line data bus.
I've disconnected and reconnected them as well to make sure the connections are good and tight.
C