Thermostat underheats; room never reaches the set temperature even though heating runs for long periods.

Safety: Only basic menu changes and visual checks; turn off power if inspecting wiring.

Steps:

• Compare temperatures: Place a reliable thermometer near the thermostat. If the thermostat reads significantly higher than actual, adjust the temperature offset in settings.
• Check floor limit: For underfloor heating, verify that the maximum floor temperature limit is not set too low (e.g., 25°C). Increase within safe limits if necessary.
• Inspect heating system: Ensure all radiators or floor zones are warming evenly. Cold sections may indicate airlocks or failed elements that need plumbing or electrical repair.
• Increase setpoint temporarily: Raise the setpoint by a few degrees to test whether the system can reach a higher temperature at all.

Resolution: Correct sensor placement and settings. If the thermostat is reading correctly but the room still underheats, the issue is with the heating system capacity, not the thermostat.