Room thermostat display shows F.01 and will not control heating

Safety first: The room thermostat is low voltage, but it is connected to a boiler control circuit. Before opening any wiring center or boiler casing, isolate mains power at the fused spur and verify with a suitable tester. Do not remove the boiler combustion cover.

Checks:

• Power‑cycle the thermostat: remove it from the wall plate (if it is a plug‑on type like Glow‑worm MiGo or Climastat RF), wait 30 seconds, then refit and allow it to reboot.
• Check ambient conditions: ensure the thermostat is not installed above a radiator, in direct sunlight, or in a draught, which can cause sensor over‑range and trigger F.01.
• Inspect the thermostat housing for signs of condensation or water damage. If moisture is present, allow it to dry fully and correct the source of moisture (e.g. bathroom steam, leaky window).
• If the thermostat has a service menu, run the built‑in sensor self‑test (refer to the Glow‑worm control manual). If the internal temperature reading is wildly inaccurate (e.g. 0 °C or 99 °C), the NTC sensor is likely failed.

Remedy:

• There is no field‑replaceable internal sensor on most Glow‑worm smart thermostats. If F.01 persists after a reset and relocation, the complete thermostat head must be replaced.
• Record the current settings (schedules, Wi‑Fi details) if possible, then fit a new compatible Glow‑worm smart thermostat and re‑pair it with the boiler or internet gateway according to the installation manual.
• If the thermostat is under warranty, contact an authorised Glow‑worm service partner rather than opening the casing.