And please don’t cite Rossi’s idiotic claim, written semi incoherently, that the high temperature would hurt the heater. If that’s true, why is it OK if the same temperature is reached by a reaction rather than Joule heat? What’s the difference?
The difference might be that heat from a reaction comes from a larger mass of material, so the average temperature of the material is lower. The Joule heater wire might be smaller than the reactant in the tube, so it would get hotter, and melt.
I am not saying this was the situation; I am saying this is plausible. If that is the case, it is no way to design the experiment. You need more heater wire.