Actually, when I checked the system for your question, I noticed that I now have temperature graph (from last 7 days only, but nothing beyond that, don't know why). It's quite obvious that I cannot get graph from fan state, which is no a "value". So maybe there is nothing wrong with system anymore. I just don't know what has happened since I last time checked that graph and it didn't work (probably couple of weeks after NPM update, in early summer.)
All I now need is to upgrade all Catalyst 2950 switches to 2960 which gives me temperature information. 