The main problem is that the heater says powered long after the pump stops, causing an OHH error.
This video is me narrating to myself as I try to focus my troubleshooting. I believe the "sparks" as the relays open are normal. If I had waited a few more moments I would've seen sparks on K6 & K7, which are the high limit relays. So the water in the heater tube boils (as you can hear in this clip) but then the high limit relays cut the power to the tube as they should.
The OHH error resulted in a safety lock-out (not proper term, I'm sure) otherwise I would've shot the video again.
It seems that the sensor probes are doing what they're supposed to do, but they don't do it fast enough, resulting in an OHH.
![](https://s2.save4k.ru/pic/2BYrtijrJ2k/maxresdefault.jpg)