Flushed radiant water heater, now confused

Whoops. I have just flushed out the water heater for the radiant system. However, the water flow wasn't what I expected, so now I'm not certain how to make sure the water heater has no air pockets. Also, I'm not sure whether I need to purge air from the system itself. And for that matter, how to do either. The components are:

- Fed by domestic with backflow prevention valve
- Single zone, 6 PEX manifold
- Just one drain value (not counting water heater drain) at the manifolds
- Pressure tank and pump
- Water heater
- A Motorola valve I can set to "open"

Any help appreciated. I've been reading some materials here and other sites but can't quite figure it out. Many thanks!

UPDATE--The system has an auto purge, so when I filled the water heater and turned on the circulation pump, there was much hissing and gurgling, gradually getting very quiet. I can't see or hear any air in the system. Am I safe? Is there still a chance of air pockets in the water heater (nonononono) or radiant PEX?

If the water is circulating (and that's a big if in the pex lines), then any residual air trapped there will be pulled out by the air scoop extraction device. Depending on the elevation differences, it can sometimes be a pain to get all of the air out of loops.