Radiators are only lukewarm and the boiler cycles on and off rapidly.

Safety: Allow the system to cool before handling filters or valves.

• Check room controls: Ensure thermostatic radiator valves are open and the room thermostat is set above current room temperature.
• Clean system filter: If a magnetic or mesh filter is installed on the return to the CTC boiler, isolate, depressurise locally, and clean the filter element.
• Adjust pump speed (technician): Increase the pump speed setting to improve circulation through the system.
• Balance radiators: Throttle back lockshield valves on radiators closest to the boiler to encourage flow to distant radiators.
• Check boiler modulation settings (technician): In the installer menu, verify that maximum output is correctly set for the system size to reduce short cycling.