Thermostat calls for heat but boiler does not start; receiver LED indicates demand.

Safety first: Isolate power to the boiler before opening its front panel or touching any internal wiring.

• Check boiler terminals: Verify that the Delta Dore receiver’s COM/NO contacts are wired to the correct external thermostat terminals on the boiler.
• Continuity test: With power off, test continuity of the control cable between receiver and boiler using a multimeter.
• Boiler settings: Some boilers require enabling external thermostat control in their menu. Check the boiler manual and enable this option if needed.

If wiring and settings are correct and the boiler still does not respond, the boiler’s control board may be at fault and a heating professional should be consulted.