I remember Kim and Aggie(y?) on How Clean is your House, once showed a fantastic way to clean pots and kettles (the ones that sit on your stove top not 'modern' plastic ones).
The ones at work are looking really digusting - I kid you not when I say a piece of limescale 5mm thick fell out the other night and if we have a quiet night (as most have been so far) I want to have a go at them if I've got time - as the urn is still broken - and the thought of the residents drinking their morning tea out of those is horrible.
I have distant thoughts that perhaps white vinegar was involved somehow.......