Thermostat display is completely blank and unresponsive

Safety: Before checking fuses or wiring, switch off the main isolator and verify absence of voltage with a suitable tester if you are competent to do so.

• Check other devices: Confirm that the boiler and other appliances on the same circuit have power. If not, reset the breaker or replace the fuse.
• Inspect fused spur: If the thermostat or boiler is fed via a fused spur, check and replace the fuse (typically 3 A) if blown.
• Verify adapter: For plug-in powered thermostats, test the adapter on another device or measure its output.
• Check base connections: Remove the thermostat from its base and ensure the low-voltage wires are firmly clamped in the correct terminals.

If power is present at the base but the thermostat remains dead, the thermostat electronics are likely faulty and the unit should be replaced.