Carrier 58MVC Error Code 23: Pressure Switch Did Not Open
What Does Code 23 Mean?
During its start-up sequence, the 58MVC's control verifies that the pressure switches are in the correct state before and as the inducer builds draft. A pressure switch should be open at rest and close once the inducer establishes proper draft. Code 23 is set when a switch that should be open is instead reading closed — it did not open when expected.
The two causes the manual lists are obstructed pressure tubing and a pressure switch stuck closed. If the small tubing between the inducer or pressure taps and the switch is blocked or holds residual pressure, or if the switch diaphragm is mechanically stuck, the board sees a switch that never opens. Because the control uses this open/closed sequence as a safety proof, a switch stuck closed defeats that check, so the board flags the fault rather than firing.
This is different from codes 31, 32, and 43, which report switches failing to close or disagreeing with each other. Code 23 is specifically about a switch failing to open, which points to a stuck switch or a tubing obstruction holding it closed.
Inspecting and clearing internal pressure tubing and testing or replacing a pressure switch are inside-the-cabinet tasks that require a technician; they are not homeowner-serviceable.
What You'll Notice
- The furnace fails to start a normal heating sequence
- The furnace may not begin its ignition sequence at all on a call for heat
- Repeated failed starts or short-cycling
- Little or no heat despite the thermostat calling
- The problem may follow recent service where tubing could have been pinched or misrouted
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Obstructed pressure tubing | Common | ✗ Call a pro → |
| Pressure switch stuck closed | Common | ✗ Call a pro → |
How This Is Diagnosed
A technician verifies the state of the pressure switches during the start-up sequence and identifies which switch is failing to open. They inspect the associated pressure tubing for obstruction, kinks, or residual moisture, and test the switch itself for a stuck-closed condition.
Depending on the finding, the repair is clearing or replacing the tubing or replacing the pressure switch. This work is inside the furnace cabinet and involves safety-critical components, so it is professional work rather than a DIY task.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- Contact a technician — a pressure switch that will not open needs internal inspection of the switch and its tubing
- If the code appeared after recent service, have the installer confirm the pressure tubing was routed correctly
- Do not attempt to open the cabinet to service the pressure switches or tubing yourself
- If the furnace repeatedly fails to start, leave it off and call for service to avoid stressing components
Frequently Asked Questions
What does 'pressure switch did not open' mean on a 58MVC?
It means a pressure switch that should be open at the start of the cycle is reading closed. Usually the tubing is obstructed or the switch is mechanically stuck closed, and the board halts start-up as a safety check.
How is code 23 different from the other pressure switch codes?
Codes 31, 32, and 43 involve switches failing to close or disagreeing. Code 23 is the opposite problem — a switch failing to open — which points to a stuck switch or a tubing obstruction holding it closed.
Can I fix code 23 myself?
No. Inspecting internal pressure tubing and testing or replacing a pressure switch are inside-the-cabinet tasks that require a technician. There is no safe homeowner fix for this code.
✓ Verified against manufacturer service manual — March 2026