Furnace displays E08 and will not respond to thermostat commands.

Safety: Turn off furnace power before working on low-voltage wiring to avoid shorting the control transformer.

Steps:

• Check control fuse: Locate the low-voltage fuse (often 3–5 A automotive-style) on the Atlantic control board. If blown, replace with the same type and rating. If it blows again, there is a short in the 24 V circuit.
• Inspect thermostat cable: Check the cable from the furnace to the thermostat for damage (staples through the wire, crushed insulation). Repair or replace as needed.
• Verify thermostat wiring: Confirm that R, W, Y, G, and C (if used) are correctly connected at both the thermostat and furnace terminals according to the Atlantic wiring diagram.
• Bypass thermostat (test only): With power off, remove the thermostat wires at the furnace. Restore power and briefly jumper R to W at the control board. If the furnace starts normally, the thermostat or its wiring is suspect. Remove the jumper after testing.

Note: Do not leave jumpers in place for normal operation. If you are unsure about wiring, consult a professional.