Virginiafiretruck,
I feel like I'm on a chat line. That is a possibility. When a fresh engine is filled for the first time, the system will invariably have air pockets and bubbles in it. This is part of the mentality behind drilling the little hole in the thermostat flange.
The hole allows trapped air and small amounts of coolant to sneak by and purge the system. Your heater would have to have a shutoff valve of some sort in one of the lines, or it would be in the loop at all times.
What happened to you with the over temp is one of the most common ailments of a new start-up. It is VERY minor, you were sharp enough to catch it, and it is probably cured as I type.
Stuart
