Trane · Furnace

E27 Return air thermistor out of range or not connected

Low severity Trane S8V2

What the control is telling you

The return temperature sensor in the blower harness is open/shorted or enabled but not connected. Furnace still runs.

Applies to: Trane S8V2 only

Likely causes

Open or shorted thermistor
Harness damage
IFC input fault

Test and repair steps

Warning: Turn off power before unplugging connectors or measuring resistance.
Option disable return temperature in the diagnostics app or with Menu/Option (24 V mode only) to clear.
Remove the 12-pin blower harness and read resistance between GY/56 and GY/57; compare to the thermistor table. Open or short: replace the blower harness.
Unplug connector E21 (RET_T) and check about 3.2 VDC between its pins; under 3 VDC means replace the IFC.

Settings for these units

Clearance to combustibles · Trane S8V2

Cabinet width	Vertical sides / top	Horizontal sides / top
14.5 in.	0 / 1 in.	1 / 2 in.
17.5 in.	0 / 1 in.	1 / 2 in.
21.0 in.	0 / 1 in.	1 / 3 in.
24.5 in.	0 / 1 in.	1 / 5 in.

24 in. front service access.

3 in. in front of the combustion air openings.

Return filter size by cabinet width · Trane S8V2

Cabinet width	Filter
14-1/2 in.	1 - 14 x 25 x 1 in.
17-1/2 in.	1 - 16 x 25 x 1 in.
21 in.	1 - 20 x 25 x 1 in.
24-1/2 in.	1 - 24 x 25 x 1 in.

Filters are field supplied and mounted outside the cabinet.

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

Models that show this code

12 models in Trane S8V2

S8V2A040M3PCBS8V2A040M3PDS8V2B060M4PCBS8V2B060M4PDS8V2B080M4PCBS8V2B080M4PDS8V2C080M5PCBS8V2C080M5PDS8V2C100M5PCBS8V2C100M5PDS8V2D120M5PCBS8V2D120M5PD

Other codes on the same units

E13 Blower motor size / OEM ID mismatch
E14 Configuration file error
E17 Blower motor communication error
E23 Menu data not received by combustion micro (CCM)
E24 Internal communication error between ACM and CCM
E25 Orientation sensor out of range
E26 Return static pressure sensor out of range or not connected
E28 Supply air thermistor out of range or not connected

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Source: Trane FNR-SVX003A-EN (S8V2 installer's guide) - section Integrated Furnace Control Display Codes, Table 37 Error codes; Trane FNR-SVX003A-EN (S8V2 installer's guide) - section Troubleshooting (flowcharts). Summarized in our own words; check the original manual for your model.

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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.