Hey KC
I see that your home port is Portland. If you are there I can direct you to a good Aqua Hot place up the I-5.
Sounds like it is a simple fix. Perhaps a connection was left undone after winterizing last year.
When you flushed the system out did you make sure all the circuts in the water manifold for low point drains were turned off? If you can see a small pipe where the water is running out that might be it!
I hate using that pink antifreeze. I have gotten by with a couple heaters but in Portland you get colder than we do in Port Angeles.
Just in case you want to know. Look up
www.brazelsrv.Com . They are in Centralia, wa. Ben is their Aqua Hot trained guy. They even have a great little park for you to stay in.