These ports do seize up but that shouldn't have happened so soon.
Personally I don't bother with boiler cover (it's still under warranty actually) but I do have 2 or 3 plumbers/heating engineers that I know would turn up at short notice. Last time I needed one he came within 2 hours. I save the money on paying for the cover to pay the infrequent visits of the plumbers. I do make sure that it is thoroughly serviced annually.