I've had a hotbin for about 6 months and only recently got the hang of it. Had some success with grass, leaves, bulking and paper but that stopped after a few days - temp went up to 60 and then back down to ambient a few days later.

I cracked it over winter when it was snowy! Bin was cold so just decided to empty out the leachate and noticed a few hours later the temp had risen ever so slightly. Kept emptying the leachate 3 times a day and it got hotter and hotter! Eventually I just left the blue cap off and put a takeaway tub under the nozzle - no more leachate and it's running at about 60! I can only assume the grate is blocked up.

Hopefully this helps someone else too!