E08 Low flame signal (still running)

What the control is telling you

Flame current is weak but still high enough for the furnace to run. The S8V2 flowchart treats under 0.5 microamp as the trigger. Fix it before it turns into ignition lockouts.

Applies to: Trane S8V2 (80%, 2-stage, variable speed, Link) and S8B1 / S8X1 / S8X2 (80%, 1- and 2-stage)

Likely causes

• Dirty or oxidised flame sensor
• Sensor mispositioned
• Poor ground or loose sensor wire

Test and repair steps

1. Start 1st stage heat and let flame establish.
2. Set a meter to DC volts across the FP pads on the IFC (1 VDC = 1 microamp); 0.75 to 3.0 is normal, readings vary with meter type.
3. If under 0.5, check sensor position against the manual figure and correct it.
4. Clean or replace the sensor; check its wire and the burner ground.
5. If the reading is good, look for loose wiring or connections.

Settings for these units

Clearance to combustibles · Trane S8V2

24 in. front service access.

3 in. in front of the combustion air openings.

Return filter size by cabinet width · Trane S8V2

Filters are field supplied and mounted outside the cabinet.

Over 1600 CFM upflow: return on both sides, one side plus bottom, or bottom only.

• Return filter size by cabinet width · Trane S8B1, Trane S8X1, Trane S8X2

Models that show this code

37 models in Trane S8V2, Trane S8B1, Trane S8X1, Trane S8X2

Other codes on the same units

• E6.2 Ground not detected
• E6.3 Igniter open or igniter relay fault
• E7.1 1st stage gas valve (MVL) powered with no call
• E7.2 Redundant relay (HLO output) on with no call
• E11 Gas valve relay / valve circuit fault
• E12 Control fuse open
• E13 Blower motor size / OEM ID mismatch
• E14 Configuration file error