An electronic device provides the means for back-up automatic low water cutoff. When water levels fall below a safe operation level, the boiler is de-energized. A sensing device detects current flow between a submerged probe and the shell. This unit is useful as a backup to the primary low water cutoff control. For use on SSB boiler (which use deionized, demineralized or distilled water), specify System No. SB81017. Add suffix MR for manual reset.