All of this means they don't know why it's heating up ~ even though there is much speculation in that regard.
Temperature eventually rose to 91-94 C, then Tepco did a resistance test on the Thermocouple sensor, and then it went bat crazy. Starting reading 260-280 C. Looks like something is causing temperature sensors to fail within Reactor #2. They had a similar problem in January. A temperature sensor in the lower section of the RPV rose to about 140 C, then started reading negative temps.
So temperature sensors within reactor #2 are failing after reading high temps. Tepco is losing the ability to determine what is happening within the RPV of reactor #2.