One technique for unclogging a hot tip is to heat it up and then dipping filament into it, pulling it back out and clipping the molten part off. If there is a metal burr that won't go through the nozzle opening, you might capture it with the molten plastic and pull it back out.
I do this about 5 times, and then I try to push hard enough to get plastic through the tip.
This technique will also indicate if your tip is getting hot enough to melt the plastic.