Trane · Furnace

E4.1 Reverse airflow limit open

High severity Trane S8V2

What the control is telling you

A reverse airflow switch tripped from heat building up at the blower end, usually when the blower stops too soon.

Applies to: Trane S8V2 only

Likely causes

Blower shutting off during the heat cycle
Heat off delay too short
Loose blower motor harness
Faulty switch

Test and repair steps

Warning: Never leave a limit switch jumpered; jumpers are for brief testing only.
Watch a full heat cycle and confirm the blower runs the whole time.
If the blower stops early, check the motor harness connections.
If the switch trips after the burners shut off, lengthen the heat off delay (HOd).
Replace the switch if it opens below its rated temperature.

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

E3.2 1st stage pressure switch (PS1) open when it should be closed
E3.3 2nd stage pressure switch (PS2) closed when it should be open
E3.4 2nd stage pressure switch (PS2) open when it should be closed
E4.0 Main high limit open
E4.2 Flame rollout switch open
E05 Flame sensed when no flame should be present
E6.1 120 V polarity reversed
E6.2 Ground not detected

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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.

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.