E3.1 1st stage pressure switch (PS1) closed when it should be open

What the control is telling you

PS1 was already made before the inducer started. The switch is rarely the cause; check wiring and tubing first.

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

Likely causes

• Wrong wiring or hose routing on PS1
• Welded/stuck switch contacts
• IFC sensing fault

Test and repair steps

1. Check PS1 wiring and hose against the wiring diagram.
2. With no inducer running, measure across PS1 (orange to yellow): 0 V means it is closed when it should be open.
3. If it reads closed with the inducer off, replace the pressure switch.
4. If the switch reads open but the error stays, check for voltage at IND-LO to IND-N with no call; voltage there means the IFC is driving the inducer - replace the IFC.

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

• E01 Furnace control internal failure
• E2.1 Ignition retries exceeded - flame never proven (1 hour lockout)
• E2.2 Flame recycles exceeded - flame lost after lighting (1 hour lockout)
• E2.3 1st stage gas valve not powered when it should be (10 times)
• 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
• E04 Open limit (main limit, rollout or reverse airflow)