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Thermostat - '99 A4 2.8L - Issues

So I just spent 3 evenings and 7 beers taking apart the front end of my Audi to replace my thermostat (before job symptoms were periodic heat & reservoir overflow when there was no heat) . After replacing I got heat for ~30 seconds, on par with the initial conditions. Worried, I tested the old thermostat. It failed with flying colors in water very near 212 deg. F. Therefore, replacing the thermostat should have cured the issue. Thoughts, please?

Do I maybe have air in my system? How does one bleed a coolant system?