Carrier furnace Status code 23: Pressure switch did not open
Code 23 means the pressure switch was found closed when it should have been open. Carrier's documented causes are obstructed pressure tubing and a switch stuck closed.
Applies to: Carrier 58MCB four-way multipoise condensing gas furnaces and related models using the same integrated furnace control. Bryant and Payne furnaces of the same generation use the same control and code set.
What it means
The pressure switch proves the inducer is moving air before gas is released, and it must be open when the inducer is off. The control checks this, because a switch stuck closed would prove a draft that does not exist — allowing the furnace to fire into a flue that may be blocked. Carrier documents two causes for the check failing: obstructed pressure tubing, which can hold pressure against the switch, and a switch whose contacts are stuck closed. Both mean the same thing operationally: the interlock cannot be trusted, so the furnace does not proceed.
Most common causes
- Obstructed pressure tubing, which Carrier lists first.
- A pressure switch stuck closed, with contacts that no longer open.
- Water in the pressure tubing or the tap, holding the switch closed.
- Tubing pinched or kinked during service.
- A short in the pressure switch wiring, electrically indistinguishable from closed contacts.
How to diagnose it
- Note whether the inducer starts at all. On this fault it usually does not, because the control stops before that step.
- Note whether the furnace was recently serviced. Tubing disturbed during other work is a frequent trigger.
- Check the condensate drain for backing up, since water in the tubing is a common cause on condensing furnaces.
- Distinguish this from code 31 carefully — they are opposite halves of the same test and lead to different repairs.
How to fix it
- Clearing a blocked condensate drain is reasonable homeowner work and addresses one of the causes.
- The pressure switch, its tubing, and its wiring are technician work. The switch proves safe venting, and a furnace running with it defeated can vent combustion products indoors.
- Never jumper a pressure switch. It is the interlock preventing the furnace firing into a blocked flue.
- Replace a failed switch with the exact part for the model. Setpoints are model-specific.
Notes
Codes 23 and 31 are the two failure directions of one test. Counting the flashes accurately matters more here than almost anywhere else in Carrier's code set, because the two point at opposite conditions.
Related
- Status code 31 — Pressure switch did not close, or reopened
- Status code 24 — Secondary voltage fuse is open
All codes for this manufacturer
Carrier, Bryant and Payne furnace status codes — every code, with what differs between models.
Do it yourself or call a technician?
The homeowner share of this code is exactly one subsystem: condensate. Water backed up into the pressure tubing will hold the switch closed, and clearing a blocked condensate drain and trap is reasonable homeowner work on most installations, with no gas-side components involved. Everything else is professional — the tubing runs, the switch itself, and the wiring short that is electrically indistinguishable from stuck contacts. The temptation specific to this code is also the worst one available: a switch that seems merely stuck closed invites a bypass to get heat back, but the open state is how the control proves the flue was clear before releasing gas. Jumper it and the furnace will happily fire into a blocked flue. If condensate and a recent-service disturbance both come up empty, the rest is a technician's morning.
The same fault on other brands
A pressure switch found closed before the inducer starts is a defeated interlock in every brand's language: Goodman's 2 flashes, Lennox alert 224, Trane's E31, and Rheem's 4 blinks — switch remains closed. The pressure switch codes hub tracks 47 pressure-switch codes across 12 control families and keeps this stuck-closed family separate from the far more common stuck-open one — which on this Carrier control is code 31, the opposite half of the same test.
What the fix costs
The repair cost guide prices a pressure switch at $150–400 installed, and its attached note — check for a blocked flue first — describes this fault family exactly: the part is frequently not the fix. Obstructed or waterlogged tubing costs a technician's time rather than a component, and when the blockage traces back to the condensate system the bill can stop at the $75–150 diagnostic, often credited against work done. The genuinely-stuck-contacts outcome sits toward the top of the range because the replacement must be the correct switch for the model — setpoints are model-specific, which is also why a universal-part bargain is the wrong instinct here.
What this looks like
From the outside, this usually shows up as the furnace starts and stops in short bursts — that walkthrough covers what to check in order, and when it stops being a homeowner job.