Darcy,
If it's at all possible try taking your external sensor a little closer to the console, it could be that the distance is a problem, especially if the weather is cold. When renewing batteries in external sensors, replace with Lithium they work better at lower temperatures.
If that fails it sounds like your sensor has had it. I'm waiting for Oregon to replace the Anemometer for my WMR100 after less than a year.
Alan