Dettson furnace control board shows E6; blower may run continuously and furnace will not heat.

Safety first: Turn off power to the furnace before touching any wiring.

• 1. Inspect thermostat connections at furnace: Remove the blower door to access the control board. Verify that R, W, G, Y (and C if used) wires are firmly attached and not shorting against the cabinet or each other.
• 2. Check thermostat cable: Follow the thermostat cable from the furnace entry point. Look for staples driven through the cable, crushed sections, or rodent damage. Repair or replace damaged cable.
• 3. Confirm thermostat wiring at the wall: Remove the thermostat from its base and verify wires are connected to the correct terminals per Dettson and thermostat manufacturer instructions.
• 4. Test transformer output: With power on (exercise caution), measure voltage between R and C at the control board using a multimeter. It should be around 24 VAC. If there is no voltage, the transformer or primary power feed may be faulty and should be replaced by a technician.
• 5. Reset control: After correcting wiring issues, cycle power to the furnace and call for heat. If E6 persists, the control board may be damaged and require replacement.