Everything is fine. He does what I wanted. The contact remains closed until the temperature rises to the set trip level, then the contacts open. It has more hysteresis curve than I like (open the switch in the off position, but it's too cold than I'd like before it closes the switch again). Not sure if I want to trust my boiler (bomb) only to this unit, so I'll switch to a digital controller and leave it in place for level 2 protection at a slightly higher temperature.
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