NickA - thanks for the "heartwarming" news. At least yours was under warranty.
I just found out the circulation pump is $200+. (WOW!) Even on auction and other web sites it's at least that much. (Laing Thermotech SM-909-NHW-18 3/4.)
For that price, I guess I want to make very sure it's the circ. pump before I spring for a new one. I feel confident I can replace it on my own. But for fun, I'll call my dealer and get a service estimate.
If anyone cares to recommend a good circ. pump source with reasonable prices, feel free to message me.
Thanks everyone.