Safety: Isolate power before working on control wiring.

Check thermostat location: Ensure the CTC room sensor or thermostat is not near heat sources, direct sunlight, or draughts.
Verify setpoints: Confirm that the room temperature setpoint and schedules are correctly programmed.
Test thermostat (technician): Bypass the thermostat at the boiler terminals to see if the boiler stops. Replace the thermostat or controller if it fails to open the circuit when satisfied.
Adjust control parameters: In the installer menu, fine-tune weather compensation curves or hysteresis settings to reduce overshoot.

Boiler runs continuously and overshoots the room temperature setpoint.

Possible Causes