Boiler shows thermostat or room control fault, will not respond to demand

Safety: Isolate power before working on control wiring.

• Check programmer: Ensure the timeclock or programmer is set to ON or a timed period that should be active. Replace batteries if it is battery-powered.
• Room thermostat: Turn the room thermostat up to maximum and listen for a click. If no click, the stat may be faulty.
• Boiler demand indicator: Many Riello boilers show a demand icon when a call for heat is present. If absent, the issue is likely external controls.
• Bypass test (qualified person): A competent person can temporarily link the thermostat terminals at the boiler to confirm if the boiler fires, indicating a control circuit fault.