Just recently, the hot water has been dropping off a cliff. The reading drops from 50ish to 20ish in just 5 minutes. There have been three showers, so enough to drain it. Anyone else has this? Curious why it doesn’t drop gradually.
I suspect this is probably just down to temperature layering, Chris.
Showers (but maybe not power showers) draw water off from the tank top relatively slowly, and the cold water entering at the tank bottom just stays there - at the bottom - rather than mixing throughout the tank, because cold water is denser.
The cold/hot interface rises slowly with each shower until finally it gets to the thermocouple location and bingo the water suddenly shows up as cold.
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This is quite normal, as the temperature sensor is probably at the bottom of the tank, and cold water rushes as hot water is drawn from the top. As you’ve experienced, there’s still plenty of hot water at the top even when the temperature at the bottom is reading 17°.
(Sarah explains it better)
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Thank you both 
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Is that a third party sensor on the top of the tank?
Yes, just a DS18B20 connected to an ESP32 microcontroller running ESPHome.
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