Thermostat is completely dead: no display, no LEDs, and no response to button presses.

Safety: This may involve mains voltage. Turn off power at the main switch or breaker before removing covers.

• Check other devices: Confirm whether the boiler and other controls have power. If not, reset the relevant breaker or replace the fused spur fuse with the correct rating.
• Inspect control module: Verify that the Ngenic control module near the boiler has power (LEDs lit). If not, check its supply wiring and fuse.
• Check thermostat wiring: With power off, remove the thermostat from its wall plate and ensure the low-voltage wires are firmly connected and not damaged.
• Test with known-good power (advanced): If you have a compatible 24V source, you can test the thermostat off-wall to see if it powers up.

If the thermostat remains dead with confirmed power at its terminals, the internal electronics are likely faulty and the Ngenic thermostat unit should be replaced.