Amp keeps shutting off

I have the Schiit Vidar powering two 98db 1w/1m speakers. This thing will turn into fault mode so quick once turned up. Only using 4-10 watts per channel, it will turn off after 20min with a box fan blowing on it. I took the cover of the amp off, which I didn't want to do, and that didn't help at all (again with a box fan blowing on it). Once using anything above the 30 watt per channel range, the thing will last 1 minute before shutting off (although that 1 minute sounds really good). The amp is rated for 100w RMS per channel into 8 ohms. I'm not expecting it to actually sustain that rated power, but come on. Why isn't it at least sustaining 20 or 30 or even 10? Am I doing something wrong? Or am I out of luck?