Status LED flashes eight times, furnace may not respond to thermostat calls.

Safety First: This involves line voltage. If you are not experienced with electrical work, do not proceed. Turn off power at the breaker before opening the electrical compartment.

This code indicates an electrical supply or grounding problem.

• Verify power supply: Check that the furnace service switch is on and the breaker is not tripped. Reset if necessary.
• Inspect wiring connections: Remove the blower door and access the control board. Verify the L (hot), N (neutral), and ground wires are firmly connected and not burned or loose.
• Check transformer output: With a multimeter and power on (advanced users only), measure between R and C on the control board. It should read around 24 VAC. If low or zero, the transformer may be faulty.
• Inspect thermostat cable: Look for damaged or pinched thermostat wires between the furnace and thermostat. Shorts between R and other terminals can cause control issues.

When to call a professional: For any uncertainty with line voltage, transformer replacement, or board diagnosis, contact a licensed HVAC technician or electrician.