Room thermostat calls for heat but the furnace does not respond; display shows standby, no error code.

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

Steps:

• Verify thermostat mode: Ensure the thermostat is set to HEAT and the setpoint is above room temperature.
• Check wiring: Inspect the thermostat cable for damage and confirm correct connections at both thermostat and furnace terminals.
• Bypass test (advanced): Temporarily bridge the heat call terminals at the furnace (per Cointra wiring diagram). If the furnace starts, the thermostat or cable is faulty.

Professional help: If the furnace still does not respond, the control board input may be defective.