Thermostat powers on but does not call for heat even when room temperature is well below setpoint.

Safety first: Output testing may involve live circuits. Isolate power before removing covers or accessing wiring.

Steps to diagnose and fix:

• 1. Check mode and schedule: Ensure the thermostat is in HEAT mode and not in OFF, ECO, or holiday mode. Review the daily schedule to confirm that the current time period has an appropriate setpoint.
• 2. Adjust setpoint: Temporarily raise the setpoint by 3–5°C above room temperature and wait a few minutes to see if the heat demand icon appears.
• 3. Review advanced settings: In the installer menu, check hysteresis/deadband and minimum on/off times. Extremely wide settings can delay heat calls.
• 4. Listen for relay click: When calling for heat, listen for a relay click inside the thermostat or wiring centre. No click may indicate a failed relay or triac.
• 5. Test output at terminals: With appropriate safety precautions, measure voltage at the boiler/actuator output when heat is demanded. If no change occurs, the output stage is likely faulty and the thermostat or wiring centre should be replaced.

When to call a professional: If configuration appears correct but no heat demand is generated, a technician should test and possibly replace the control hardware.