Room temperature does not reach setpoint even though the Vaillant smart thermostat shows heating as 'ON'.

Safety: Radiators and pipes may be hot; take care to avoid burns. Isolate power before working on valves or wiring.

• 1. Check thermostat settings: Verify the setpoint temperature and schedule. For weather‑compensated systems, review the heating curve and increase it slightly if rooms are consistently cool.
• 2. Inspect TRVs and radiators: Ensure thermostatic radiator valves are open in the affected rooms. Bleed radiators to remove air if they are hot at the bottom and cold at the top.
• 3. Check boiler flow temperature: On the Vaillant boiler, confirm the CH flow temperature is not set excessively low. Increase within safe limits recommended by Vaillant.
• 4. Verify zone valves/actuators: Ensure the relevant Vaillant zone valve or manifold actuator opens when the thermostat calls for heat. Replace any actuator that does not move or fails to open fully.
• 5. Consider system balancing: If some rooms heat well and others do not, have a heating engineer balance the system by adjusting lockshield valves.