DS18B20 Not Found

Been doing some experiments with a DS18B20 sensor on an Espruino WiFi, I've had a couple of successful reads but mostly I'm getting this error:

(Sorry for the screenshot I can't figure out how to copy/paste from the console!

My code is just this for now:

var ow = new OneWire(A0);
var sensor = require("DS18B20").connect(ow);

function read(){
  sensor.getTemp(function (temp) {
    console.log("Temp is "+temp+"°C");
});
}

1 Attachment