Trane · Furnace

8 Flashes Low flame sense signal

High severity AUH1B

What the control is telling you

Flame sensor signal is weak.

Applies to: Integrated furnace control

Likely causes

Low flame sense signal

Settings for these units

Clearance to combustibles · Trane S8V2
Return filter size by cabinet width · Trane S8V2
Return filter size by cabinet width · Trane S8B1, Trane S8X1, Trane S8X2
Return filter size - upflow and downflow · Trane S9X1, Trane S9X2, Trane S9B1
Clearance to combustibles · Trane S9X1, Trane S9X2, Trane S9B1
Return filter size - upflow and downflow · Trane S9V2

Other codes on the same units

2 Flashes System lockout
3 Flashes Draft pressure error
4 Flashes Open high limit device
5 Flashes Flame sensed with no flame expected
6 Flashes 115 V AC power reversed or poor grounding
7 Flashes Gas valve circuit error
9 Flashes Ignitor circuit or neutral-to-common voltage
Continuous OFF Check power

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Source: Trane installer's manual (AUH1B040A9241A), p. 39. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.