I went to remove my filter-bag (see http://forum.hotbincomposting.com/fo...?p=291#post291) and found the slots below the filter-bag were all blocked with a crystalline deposit. In fact the filter-bag was 'glued' to the base of the biofilter unit. No air could have been getting through at all. Was this why the compost was not heating? I cleaned all the slits out with a knife. The situation is see from the photograph of the filter-bag. Didn't have camera with me when I found the situation 

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