F.09
Glow-worm Internal Memory / EEPROM Error

Thermostat displays F.09 and schedules cannot be saved

Advertisements

Safety Warning

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.

Advertisements

Possible Causes

Corrupted non‑volatile memory on thermostat PCB, Power interruptions during firmware update, Age‑related EEPROM wear, Manufacturing defect in memory chip

How to Fix / Troubleshooting

Safety: Only low‑voltage handling is required. Do not open the thermostat PCB.

Steps:

  • Perform a full factory reset of the thermostat from the installer or advanced settings menu. This will erase all schedules and network settings.
  • After reset, reconfigure the basic time, date, and one simple heating schedule. Check if the thermostat can store and recall this schedule after a power cycle.
  • If the thermostat supports firmware re‑flashing via app or USB, follow Glow‑worm’s official procedure to reinstall the latest firmware.

Remedy:

  • If F.09 reappears or the thermostat cannot reliably store settings, the internal memory is defective. Replace the thermostat head.
  • Keep the new thermostat powered from a stable supply to avoid repeated brownouts that can corrupt memory.
Advertisements

Repair Difficulty

Medium 3/5

Required Part

Glow-worm smart thermostat main PCB (EEPROM/flash memory)
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements