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