OH is a measurement of the "hi-limit" sensor, indicating the water temp at the heater is higher than the temperature in the filter bay sensor. OR, on the other hand, the temp sensor in the filter bay is "Lieing" to the the electronics indicating the temp of the water is is 10° - 12° different than the sensor temp in the heater.
Could be a bad temp sensor. A test plug will confirm that right away. Secondly, you could measur ohms of both sensors which should be fairly close to each other. OH indicates they are not. It could be a legitimate error signal, or if the water is cool, a false reding because the temp sensor is bad in the filter bay.
You say the water is at 104°, did you measure the actual temperature or just the read out on the control panel?