MEDIUM URGENCY

Carrier Code 43 - Pressure Switch Calibration Faulty

Code 43 (4 short + 3 long flashes)

Pressure switch calibration fault.

Brand: Carrier (Also covers Bryant, Payne) | Equipment: Gas Furnace

What This Code Means

Code 43 on Carrier (Bryant, Payne) means the pressure switch is reading values outside its expected calibration range. Usually obstruction or switch degradation.

Likely Causes (Ranked)

Most common on 90%+ AFUE

Blocked condensate trap

What: Plugged condensate drain affects pressure readings.

How to check: Inspect condensate trap and drain.

Fix: Clear trap, flush drain line.

Common

Blocked intake or exhaust

What: Restricted venting affects pressure.

How to check: Inspect both intake and exhaust outlets.

Fix: Clear blockages.

Shop parts

Common

Failing pressure switch

What: Switch is degrading, readings drift.

How to check: Tech manometer test.

Fix: Replace switch.

Shop parts

Diagnostic Steps

Inspect intake and exhaust
Check condensate trap
Replace pressure switch if obstructions cleared
Call tech if persistent

Frequently Asked Questions

Difference between Carrier code 23, 31, 43?

23/31 are pressure switch on/off faults; 43 is calibration drift (switch operating but values off).

Same on Bryant/Payne?

Yes - identical control board.

DIY?

Vent and trap inspection yes; switch replacement straightforward.

Related Carrier Codes

Related Symptoms

Need More Help?

Try our interactive symptom diagnostic tool or browse Carrier parts.

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