Why won't my Huawei Honor 3C go to black when I hold it to my ear during a call?

[AC Question]

As mentioned I have a problem with the screen not turning black when I hold it to my ear during calls which occationally causes my face/hair to end the call/activate flightmode/things. This is very annoying and have caused problems on multiple occations and I can't find any settings which might solve my issue. Any help would be much appreciated.

 

[B. Diddy]

Welcome to Android Central! The proximity sensor might be faulty. Try testing it with an app like Sensor Box.