On the covered Carrier gas furnace, 23 means the low-heat or high-heat pressure switch was already made (closed) when the thermostat called for heat. The control flashes 23 until the switch opens, then starts the cycle. First, turn off the thermostat call, wait a minute, and start one normal heating cycle to see whether the code repeats.
Differential
Likely causes of “Carrier gas furnace code 23”, and how to tell them apart
- 1
A pressure switch stuck closed
What separates it Code 23 shows before the furnace starts
How to confirm Carrier's flowchart ends at replacing the switch or the control
- 2
A short in the switch wiring
What separates it The circuit reads closed all the time
How to confirm Technician inspection
- 3
Condensate in the tubing
What separates it The switch reads wrongly
How to confirm Technician draining
- 4
A control fault
What separates it The switch tests well
How to confirm Technician replacement
- 5
A temporary glitch
What separates it The code clears and does not return
How to confirm Run one normal cycle
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the code reads 23
- Whether it clears once the call ends
- Recent service
- The model number
Try in this order
0 of 8 completedWhat to do first
ReversibleTurn off the thermostat call, wait a minute, and start one normal heating cycle to see whether the code repeats.
Correct only the documented fault domain
ReversibleA pressure switch that is already closed before the inducer runs points to a stuck switch or a short in its wiring. Carrier's flowchart ends at replacing the low-heat or high-heat pressure switch or its assembly, or the furnace control. Never jumper a pressure switch: it is what proves the vent is drawing.
Turn off the thermostat call
ReversibleWait a minute.
Start one normal cycle
ReversibleWatch the display.
Note whether 23 repeats
ReversibleAnd when.
Do not touch the switch
ReversibleOr its tubes.
Record the date
ReversibleAnd weather.
Call a technician
ReversibleIf it repeats.
Model-specific
What is true of this model and not of its siblings
- A check before every start
- The control wants the pressure switches open at rest. If one is closed, it flashes 23 until it opens and only then starts.
- What Carrier says
- Carrier's flowchart ends at replacing the low-heat or high-heat pressure switch or assembly, or the control.
- Never jumper
- A pressure switch proves that the vent is drawing.
- Condensate
- Water in the tube can hold a diaphragm.
- A single occurrence
- If the code appears once and clears, note it and watch.
- Technician tests
- A meter, a manometer and a visual inspection.
- The switch must open first
- At the start of a call for heat, the pressure switches should be open because no air is moving. A switch that is closed at that moment is either stuck, shorted or reading a pressure that should not be there. The control flashes 23 and waits for it to open.
- Do not jumper
- It can be tempting to short the switch's terminals to get the furnace running. A pressure switch confirms that the vent is drawing exhaust out of the house. Defeating it risks carbon monoxide in the home, and Carrier says never to do it.
- What the repair is
- Carrier's flowchart ends at replacing the pressure switch or its assembly, or the furnace control. The technician decides which with a meter and a manometer. Ask whether the new switch matches the model's part number.
Stop boundary
When this stops being a self-service repair
- !Never bypass, jumper or tape over a safety switch
- !Stop for a carbon monoxide alarm, soot, scorch marks or flame outside the burner compartment
- !Call a qualified technician for anything behind the furnace's panels
- !If you smell gas, leave the building and call the gas utility from outside; do not use switches or phones inside
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 23 mean on a Carrier gas furnace?+
The low-heat or high-heat pressure switch was already made (closed) when the thermostat called for heat. The control flashes 23 until the switch opens, then starts the cycle.
Will it clear by itself?+
The control waits for the switch to open.