This error indicates there is a temperature probe failure. This particular part is the shiny chrome probe which sits in a matching round housing just below the control panel (as below)
First, turn off the power to the shower. Next, gain access to the rear of the shower and ensure the probe wire is not wrapped or caught around any hot/cold water pipes. If this is the case, clear it from the pipework, power up the unit, and check to see if the error code has cleared. This is the most common cause as the heat/cold from the touching pipe can give the probe an incorrect reading from that of in the cabin.
If this does not clear the issue, or the probe was free from any pipework, remove the probe from the housing, cup it in your hand and blow on onto the probe. The instant heat should cause the probe to activate and you will see if it's working.
If all the above fail to fix the issue, then it's likely the control panel is faulty and will need replacing. If your product is under warranty, please submit a support ticket along with your warranty number to obtain a replacement. If outside warranty, please visit our spares section where you can locate a replacement control panel.