F15 displayed; thermostat reports internal temperature sensor overheating.

Safety first: If the thermostat feels very hot, isolate power before handling.

Steps:

• 1. Check installation location: Ensure the thermostat is not mounted directly above a radiator, towel rail, or other heat source. It should be on an interior wall, about 1.5 m above floor level.
• 2. Avoid direct sunlight: If the thermostat is in strong sun for long periods, consider fitting a small shade or relocating it.
• 3. Clear ventilation: Make sure no furniture, curtains, or covers block the thermostat vents. Gently vacuum dust from around the vents.
• 4. Inspect for internal faults: If F15 occurs even in a cool, shaded location, the internal regulator or sensor may be overheating. The thermostat should be replaced.