I had attempted waiting for the fire to start by interrupting my people every time they went to turn the stove off, I waited two hours before giving up....

As far as I can tell its fairly random and the stove does not need to be on long for it to happen. In my most recent family the single person living in the house at the time started to make dinner and as she was cooking the stove caught on fire (not that she noticed), it was the first time the stove had been used too.