Thanks for your reply. I thought I had fixed it at least once by the battery out trick as you say but until you said it, I was not sure I was not imagining it.

Now it is very much permanent. I tried again just to be sure: turn off, take the battery out for the duration of my commute (about one hour), turn on again - no joy (and yes, I have checked the volume setting ).

The microphone still works though: the other side can hear me, only I cannot hear them when the sound is routed through the receiver. Loudspeaker, Bluetooth, headphones, all OK. So it might be a hardware fault, I suppose. Any good idea how I can test that?