Boiler does not respond to the thermostat; it stays off even when there is a call for heat.

Safety: Turn off power before working on low-voltage wiring.

• Check thermostat: Confirm the thermostat is set to heat mode and above the current room temperature. Replace batteries if applicable.
• Inspect wiring: At the boiler, check the thermostat or TT terminals on the Crown control. Ensure the wires are secure and not corroded.
• Bypass test: With power off, temporarily jumper the TT terminals. Restore power; if the boiler starts, the issue lies with the thermostat or its wiring.
• External controls: If a zone control panel is used, verify that it has power and is indicating a call for heat to the boiler.