Carrier · Status code
Carrier 59TN7A status code 23: pressure switch stuck closed
Major code 23 means the control found a pressure switch already closed before the inducer started, when the switch should be open. Minor 23.4 is the low-heat (main) pressure switch LPS stuck closed; minor 23.5 is the high-heat (secondary) pressure switch HPS stuck closed.
On the control
- Code
- 23
- Minor
- 23.4 · 23.5
- Door LED
- 2 short flashes then 3 long
- Controller
- 59TN7A integrated furnace control with 3-digit LCD display and door LED
- Applies to
- Carrier Infinity 97 (59TN7A)
- Manual
- 59TN7A-01SI
What each minor code says, verbatim
| Display | Manufacturer wording |
|---|---|
| 23.4 | LPS stuck closed |
| 23.5 | HPS stuck closed |
A code is a condition, not a diagnosis
A switch reported stuck closed can be the switch itself, but more often it is the sensing line: a disconnected or cracked hose letting the switch see the inducer side at rest, a collector-box port plugged so the switch holds its state, water in the hose, or a switch that was replaced with the wrong set-point. The switch is tested with a manometer against its printed break point, which on this family is stated on the switch label (for example COLLECTOR BOX-LPS or HOUSING-HPS).
Which furnaces this applies to
Documented for Carrier 59TN7A furnaces (all nine sizes) in installation instructions 59TN7A-01SI REV A, edition 06/23. The control checks that both switch contacts are open before it starts the inducer, so a switch that fails closed, a hose that is off, or a port that is blocked at the wrong time sets this code.
Scope: Carrier 59TN7A Infinity 97 furnaces with the on-board 3-digit display control. Not sure which control you have? Send us the full model number from the rating plate.
Safe things to look at first
- Read the full code on the control display through the door, including any minor digit (for example 33.2), and write it down.
- Look, without touching, for obvious conditions you can report: snow or ice at the vent terminations, water on the floor, a loaded filter, a condensate pump that is full or off.
- Note whether the furnace still heats at all, and how long it runs before the code returns.
- Note whether the furnace runs at all and in which stage, and whether the code appears at power-up or after a cycle.
Do not
- Do not bypass or jumper the door switch, limit switches, rollout switches or pressure switches.
- Do not open the burner compartment, disconnect tubing, or adjust the gas valve or gas pressure.
- Do not keep cycling power to force the furnace to relight; repeated resets hide the fault and can allow unburned gas to build up after ignition failures. If the code returns, stop and call.
Homeowner-safe checks (look and read only)
- Note whether the furnace runs at all and on which stage
- Check the vent and intake terminations for blockage
When to call a technician
- If the furnace will not heat
- If the code returns after service work
Also documented on the same controller family: Carrier Performance 97 (59TP7A).
What a technician does
- A technician checks the switch contacts with power off, inspects the hoses and ports, and verifies the switch opens at its printed break point using a manometer before replacing anything.
- The condensate path is inspected, since water in the collector box can hold a port blocked and mimic a stuck switch.
Same code, other equipment
- Carrier single-stage sibling controls (59SC6A): On the single-stage Comfort 96 label the same major code 23 covers "Stuck closed Main pressure switch" and "Stuck closed secondary pressure switch" as minors 23.1 and 23.2. Sub-code numbers differ between stages; read the label on your furnace. source
Related components and symptoms
Questions people ask
What does a stuck-closed pressure switch mean for my furnace?
The control refuses to start the burner because a switch that should be open is closed, which could let the control misread the draft condition. It is a safety check doing its job; the cause is found by testing the switch and its tubing.
Was my switch just replaced? Why does 23.5 show?
A wrong replacement switch, a hose reconnected to the wrong port, or a hose left disconnected can all produce a stuck-closed reading. A manometer test against the printed set-point settles it.
Seeing code 23 on your Carrier?
Tell us the full code, the model number and whether the furnace still heats on low. BC Wide prioritizes no-heat calls across Greater Vancouver.