I have the exact setup in my coop for my girls as in the picture. This is the second winter with the heated base so it's not an older styler one. We have had -32'C (yes, friggin cold) this winter and no ice issues. The waterer is inside the coop and at that temperature they are locked in so wind the wind isn't hitting it, but still....I would think you're having a base functionability issue. That being said, I can't see what brand yours is, and can't remember what mine is, but I would imagine they should be pretty similar.
Last winter it got -40 for three days here, and I had a layer of ice on teh top of the water aprox 3/4 inch thick, but that was only when the waterer ws full. As it got closer to the base it wasn't an issue.