Anyway, I've just come home, and the deed has been done - the fan has been re-sited by our regular Mr Fixit. Problem has gone away. Just need to fill the old mounting holes and re-paint that wall now
Might be a bit late but take it you mean the fan moves from central to right or left then back to central, if you stop the fan in central position hold the fan and manually move it to to opposite position you will here a couple of clicks the fan can be adjusted to move from centre to right to centre or centre to left to centte