In this case the cell was dismantled, the working electrode was heated and the cell reassembled.
ETA- with regard to the sulphate/citrate electrolyte, I found that it needs to be freshly made, for some reason I don't understand it still works as a plating system, but very soon becomes less effective as LEC making system.
Thanks Allan, I noticed some papers use much smaller concentrations of sulphate/citrate electrolyte in the solution than I used.
Today I made another cell with increased diameter to decrease the air gap from about 2.3 mm to 1 mm - Still no voltage measured at all.