Thermostat frequently undershoots the set temperature; room never reaches the desired warmth.

Safety first: No mains work is required.

Steps to check:

• Adjust control parameters: Increase minimum on-time and reduce cycle rate in the installer menu to allow longer heating periods.
• Relocate thermostat: Move away from cold drafts, external walls, or unheated corridors.
• Verify system type: Ensure the thermostat is configured for the correct heating system type in the installer settings.

Resolution: If the room still fails to reach setpoint with correct settings and adequate boiler capacity, the issue may be with the heating system rather than the thermostat. Have the system checked by a heating engineer.