The furnace displays E8 and will not run; this may occur after a power surge or wiring work.

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Hot and neutral reversed at the furnace junction box, missing equipment ground, shared neutral or miswired service switch, damaged integrated furnace control from miswiring.

How to Fix / Troubleshooting

High-voltage safety: This involves 120/240 V wiring. If you are not experienced with electrical work, contact a licensed electrician or HVAC technician.

Checks:

Turn off the breaker feeding the furnace.
Remove the electrical junction box cover on the furnace and inspect the wire connections: hot (usually black) to L, neutral (white) to N, and green/bare to the ground screw.
Verify that the furnace chassis is bonded to ground.
Use a plug-in outlet tester or multimeter at the service switch/outlet feeding the furnace to confirm correct polarity and ground.
Correct any reversed hot/neutral or missing ground connections.
If the wiring is correct and E8 remains, the IFC may have been damaged and require replacement.

Repair Difficulty

Hard 4/5

Required Part

Integrated Furnace Control Board

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