Thermostat display completely blank; no lights or response.

Safety first: This involves mains voltage. Turn off power at the consumer unit and fused spur before opening any covers. If you are not confident, contact a qualified electrician or heating engineer.

Steps to diagnose:

• 1. Check fused spur and breaker: Ensure the boiler/controls fused spur is switched on and the fuse is intact. Check the relevant circuit breaker or RCD has not tripped.
• 2. Inspect receiver power: Confirm that the Baxi receiver or wiring center has power (indicator LEDs lit). If not, check wiring and fuses.
• 3. Test low-voltage output: With power on and using a multimeter (if competent), measure the low-voltage output feeding the thermostat. Compare with the specified voltage in the Baxi manual.
• 4. Check thermostat connection: Remove the thermostat from its backplate and ensure the connector pins are clean and not bent. Reseat the thermostat firmly.
• 5. Try a known-good thermostat: If available, temporarily connect another compatible Baxi thermostat to confirm whether the issue is with the thermostat or the power supply.

When to call a professional: If supply voltage is present but the thermostat remains dead, the internal power circuit has failed and the thermostat must be replaced.