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American Standard E3.4: Open pressure switch, 2nd stage

Source: American Standard manual (PDF) (opens in a new tab) ↗ · Updated

Status codeE3.4American Standard
What does American Standard E3.4 mean?

Open pressure switch, 2nd stage.

Call a pro: jump to when to call a pro Equipment type: furnace
How it shows: 7-segment display on an American Standard S9V2 two-stage variable-speed furnace: E3.4

American Standard S9V2 E3.4 is an open 2nd stage pressure switch. The sequence gives PS2 45 seconds to close. If it does not, the furnace records the open switch and stays in 1st stage. On the third miss in the same heat call, 2nd stage locks out until the thermostat call ends or power is cycled. The house can still have low-stage heat. E3.2 is the 1st stage switch, which stops ignition.

Likely causes

  • 2nd stage pressure switch did not close

Safe checks for E3.4

  1. The 2nd stage sequence says if pressure switch 2 does not close within 45 seconds, the furnace declares a PS2 open error and keeps running in 1st stage
  2. If PS2 fails on the third attempt in the same heating call, the guide says 2nd stage locks out until the heat call is removed or power is cycled
  3. Techniciancheck the 2nd stage pressure switch, tubing and inducer. Tubing must rise so condensate does not enter the switch
Safety firstIf you smell gas, do not touch any electrical switch or use a phone in the building; leave immediately and call your gas supplier from outside. Turn off electrical power at the furnace switch or breaker before opening any panel, and never bypass or jumper a limit, rollout or pressure switch. Gas valve, burner, venting, wiring and control-board work should be done by a licensed HVAC technician.

Capacitors can hold a charge after the power is off. Safety terms.

When to call a pro

Call a licensed HVAC technician if the furnace will heat on low stage but never steps up, and E3.4 is stored.

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Parts & tools for this fix

Taken from this code's causes or steps. A search link opens Amazon results and does not confirm a fit. Check the model number in the manual.

Furnace pressure switch hose: guide

Technician step in this code: check the 2nd stage pressure switch, tubing and inducer. Tubing must rise so condensate does not enter the switch

Search: American Standard furnace pressure switch hoseSearch: Furnace pressure switch tubing kitSearch: Furnace pressure switch hose, general search

Furnace pressure switch: guide

In this code: 2nd stage pressure switch did not close

This one is for a technician to test or replace, so we only explain it and do not link to buy it.

Furnace inducer (draft) motor: guide

Technician step in this code: check the 2nd stage pressure switch, tubing and inducer. Tubing must rise so condensate does not enter the switch

This one is for a technician to test or replace, so we only explain it and do not link to buy it.

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Related American Standard codes

E2.2Recycles exceededE3.1Shorted pressure switch, 1st stageE2.31st stage gas valve was notE6.3Igniter faultE3.2Open pressure switch, 1st stageE7.1The 1st stage gas valve (MVL)

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