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summary: Frost night in greenhouse B (2026-02-26): timeline, cause, fix
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# 2026-02-26 INCIDENT: frost night in greenhouse B

Timeline: 03:10 frost alert (`alerting.md`), 03:25 heater found off, 03:40 heater on, 04:30 back above 6 C.
Effect: some seedling trays damaged. Cause (proven): the heater's timer reset after a power cut.
Fix: the valve and heater schedule moved to the relay board (`irrigation-valve.md`), which keeps time.
The forecast had shown -3 C (`weather-feed.md`); a forecast-based warning is now on the backlog.