I've heard my "home unit" talking to carrier wave only aircraft on two occasions. One was to me when I was a solo PPL stude on my first solo sortie outside the circuit, and the second was a few weeks ago with a similar situation to the original post above - finger problems had messed up their comms boxes
On both occasions the unit explained the speechless code they wanted used (as per cap 413..) - this took all of five seconds and confirms for both the radio failed a/c AND any other traffic what is going on.
tKF