Thermostat display completely blank and unresponsive; heating does not start.

Safety first: Always switch off power at the main breaker before removing the thermostat or opening any junction box.

• Check other devices: Verify if other devices on the same circuit have power. If not, reset the breaker or replace the fuse.
• Inspect thermostat base: Remove the thermostat front and check that supply wires are firmly connected to the L/N or 24 V terminals. Tighten any loose screws.
• Measure voltage: With a multimeter (if competent), confirm that the correct voltage is present at the thermostat terminals.
• Test with known-good power: If possible, temporarily connect the thermostat to a known-good supply to rule out wiring issues.

If power is present but the display remains blank, the internal power supply or display driver is likely faulty and the thermostat should be replaced.