HVACopediaTrane · Furnace
E3.4 2nd stage pressure switch (PS2) open when it should be closed
What the control is telling you
PS2 did not prove on a 2nd stage call (S8X2 allows 45 seconds). The furnace drops to 1st stage, retries after 10 minutes, and after the third failure in the same call stays on 1st stage.
Applies to: Trane S8V2 and S8X2 (2-stage models with PS2)
Likely causes
- Vent restriction or wrong vent size
- PS2 hose problem
- Inducer not reaching high speed
- PS2 wrong orientation or faulty
Test and repair steps
- Confirm PS2 wiring and hose routing match the wiring diagram; in most cases the switch itself is fine.
- Cycle power and call for 2nd stage heat; measure voltage across PS2 (brown to yellow): 24 V means open, 0 V means closed.
- Check the inducer runs; if not, measure about 120 VAC at the inducer motor leads - voltage present means a bad inducer, none means IFC or wiring.
- Measure the draft at the switch with a manometer and compare to the set point printed on the switch label (negative pressure, compare magnitude).
- Look for blocked or undersized vent, kinked or wet hose, then replace the switch only if draft is above the label value and it still reads open.
- Confirm PS2 orientation suits the installed position.
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.
- Return filter size by cabinet width · Trane S8B1, Trane S8X1, Trane S8X2
Models that show this code
19 models in Trane S8V2, Trane S8X2
Other codes on the same units
- E2.3 1st stage gas valve not powered when it should be (10 times)
- E3.1 1st stage pressure switch (PS1) closed when it should be open
- 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
- E04 Open limit (main limit, rollout or reverse airflow)
- E4.0 Main high limit open
- E4.1 Reverse airflow limit open
- E4.2 Flame rollout switch open
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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); Trane 18-CE14D1-1A-EN (S8B1/S8X1/S8X2 installer's guide) - section Integrated Furnace Control Display Codes, Error Codes. 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.