Since it seemed more likely than not that the outdoor sensor was the culpri= t, I located and ordered a replacement sensor. I installed batteries in the= new sensor first, then in the indoor unit. After about ten seconds, the in= door unit started to respond. Moved the sensor to it's usual outdoor locati= on, and all is back to normal.
Thanks to all who responded!
Interesting footnote: The online shop I bought the sensor from is for wine = enthusiasts. They sell the weather station to folks who want to monitor the= temperature and humidity of their wine cellar!
Art Harris