SHX55M02UC/46 BOSCH Dishwasher stalls mid-cycle

[CanadaMoose]

My dishwasher has been pausing / stalling lately and the diagnosis / repair has me stumped. The test cycle returns E1 (heater problem), and sometimes E6 (turbidity sensor). For a few months and until lately, the dishwasher has run the Power Scrub Plus program ok, but on other programs has stopped washing mid-cycle, only to finish after extended run time without a proper wash. The heater has worked fine during this time. A few days ago, even the Power Scrub Plus program started showing the same stalling behavior.

Since the heater resistance reads fine, I have replaced: thermistor, impeller jug, turbidity sensor (to address the E6 error), control board. No improvement. I'm now suspecting either the circulation pump having some kind of issue, even though it doesn't make excessive noise and seems to run fine, or the little switch that's part of the heater assembly. Parts lists only call it "switch" (part # 00426400). I suspect this switch measures that water is flowing through the heater at a minimum rate to avoid overheating.

Any suggestions?