Thermostat shows E12 and schedules cannot be saved or are lost after power cycle

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Corrupted EEPROM/flash memory, Firmware bug, Power interruptions during write operations, Failing main PCB

Safety first: No internal repair should be attempted by unqualified users.

Steps:

Perform a factory reset of the thermostat via the installer menu (note: this will erase all schedules and settings).
After reset, update the thermostat firmware if the model supports OTA updates via the Heatmiser app or NeoHub.
Re-enter schedules and monitor whether they are retained after several power cycles.
If E12 reappears or schedules are still lost, the internal memory is failing and the thermostat should be replaced.

Medium 3/5

Heatmiser Smart Thermostat Main PCB

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