The Wahoo Blue S/C sensor is a popular speed/cadence sensor combo. The latest models can be paired either via ANT+ or Bluetooth Smart (4.0), and can therefore be used with TrainerRoad for speed, cadence, and VirtualPower readings.
How to Pair Your Blue with TrainerRoad
1. Open the TrainerRoad application, and go to the Devices tab.
Make sure you scroll down to the list of Bluetooth Smart devices.
2. Click the "Pair" button that corresponds with Speed and Cadence Sensor under the list of Bluetooth Smart devices.
You will need to pair your Blue as a speed and cadence sensor even if you are using only the speed or cadence portion of the sensor.
3. Wait for your Wahoo Blue to pair with TrainerRoad.
You will likely need to pedal to "wake up" your Wahoo Blue.
4. Your Wahoo Blue is now paired!
Check Magnet Placement
The most common problem with speed/cadence sensors is magnet placement. If you aren't getting speed or cadence readings, or getting very low or very high readings, check the magnet placement on both the crank and rear wheel.
You'll want the magnet to pass right next to the sensor, but not so close that it touches.
A weak battery may not be strong enough to communicate with TrainerRoad. Try replacing the battery for a more stronger signal.
Pair with another head unit
Try pairing your speed/cadence unit with another head unit like a Garmin 500. You'll want to see if both speed and cadence readings show up. Double check to make sure that your speed source is set to your speed sensor and not to GPS.