I'll pull the shower screen and use citrus solvent to clean it tonight -- gotta get the kids to a baseball game now.
I set the pump delay to 500ms in an effort to fault trace. It exhibits the same behavior at 1000ms and 500ms. If I'm splitting hairs, the heating element turns off at 1.03 bar -- the boiler pressure does not exceed 1.04 bar, and the heating element turns back on at 0.85 bar. I haven't adjusted the boiler pressure at all.