Real mystery this one!
I have a WS2300 as a back up to my Vue. First time I have had the OFL there instead of the out temperature. I have swapped the thermo-hygro unit for a brand new one I kept as a spare, as I presumed it was that which failed on the one in use, but still OFL shows. It is not the console as the WS sends to one downstairs and one upstairs with both showing OFL. I did power off one of the consoles to see if it cleared it but still OFL. The main unit is wireless.
Any ideas appreciated.