Hi Brian and
to the forum.
Error 5 indicates that one (or more) of the
MOSFETs in the controller has failed.
Usually when this happens the wheel becomes stiff to turn, but not always.
I suggest that you send a copy of the email received from Andy Zhang to David at GoldenMotor in China
and explain that you have not had a response and see if he can help.
I also suggest that you read
this post for further information about changing the controller.
Whereabouts in the UK are you?
Alan