Furnace LED displays code 24; no response to thermostat; 24V control circuit appears dead.

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

Steps to check:

• Locate the fuse: On most Luxaire control boards, a 3–5 amp automotive-style blade fuse protects the 24V circuit. Inspect it for a broken element or discoloration.
• Replace the fuse: If blown, replace with the same amperage and type. Do not use a higher-rated fuse.
• Inspect thermostat cable: Look for bare wires touching each other or metal, especially near the furnace cabinet and thermostat. Repair or replace damaged cable.
• Check accessories: Temporarily disconnect wires to external devices (humidifier, A/C contactor, zone panel) from the control board. If the new fuse holds with accessories disconnected, reconnect one at a time to find the shorted device.

When to call a pro: If fuses continue to blow, a technician should trace the low-voltage circuit and test the transformer and connected devices.