Carrier furnace status code 31: pressure switch did not close
Carrier furnace status code 31 means a high-heat pressure switch did not close or reopened during a heat call. The owner-safe checks, and where a technician takes over.
What this means
Carrier assigns status code 31 to a high-heat pressure switch input that did not close when the control called for high or intermediate heat, or that opened during the heat cycle. It reports the state of a proving circuit, so the draft inducer, venting, condensate, tubing, wiring, and the switch itself all stay on the list until one is confirmed.
Equipment and model context
Carrier two-stage and variable-speed modulating condensing furnaces that report status code 31
- 58MVC
- 58MVP
- 59MN7A
- Infinity 98 gas furnace
This reading follows Carrier service literature for two-stage and modulating condensing furnaces that flash a two-digit status code. Single-stage models and other code numbers behave differently, and the legend printed inside the furnace door is what confirms the meaning for a given board.
What you may notice
- The control board LED flashes a three then a one, and the furnace runs the inducer but the burners do not light on a call for more heat.
- The furnace produces low heat but never steps up, or it starts a cycle and shuts down partway through.
Likely causes
- A blocked or restricted flue or intake, a sagging or water-filled vent pipe, or a plugged condensate trap can stop the inducer building the pressure the high-heat switch needs.
- A cracked or disconnected switch hose, a weak draft inducer, corroded switch contacts, or a wiring fault can leave the circuit open even when venting is clear.
Diagnostic paths
Status code 31 appears mainly in cold or windy weather
The furnace runs normally in mild conditions but throws code 31 on the coldest nights or when wind is driving against the vent termination outdoors.
Check the outdoor vent and intake terminations for frost, snow, ice, or nesting debris from a safe position. Then have a technician assess the termination height and the switch setpoint against the installation instructions.
Status code 31 repeats every couple of minutes from a cold start
The furnace tries, flashes 31, waits, and tries again on a short cycle regardless of weather, and the inducer sounds weak or labored.
Leave the furnace off and arrange service. A fast repeating 31 points at a shorted switch circuit, a failing inducer, or a blocked internal passage that a technician tests with a manometer.
On a call for high heat the control expects the pressure switch to confirm the inducer is moving enough combustion air. Code 31 is that confirmation not arriving or not holding.
- Draft inducerPulls combustion air and pushes flue gas out the vent
- Vent and intakeThe paths that must be clear for the inducer to build pressure
- Switch hoseSenses inducer pressure and carries it to the switch
- High-heat pressure switchCloses when pressure is adequate, opens when it is not
- Furnace controlWithholds high-heat ignition and flashes status code 31
| When 31 shows | More likely area | Still to confirm on site |
|---|---|---|
| Only in severe cold or high wind | Vent or intake termination restricted or affected by wind | Whether the switch setpoint is also marginal |
| Every start, any weather, fast repeat | Switch circuit short, weak inducer, or blocked passage | Which of the three, measured with a manometer |
| After recent service or a new install | Hose routing, tubing pinch, or wrong switch fitted | That the correct switch and vent length were used |
Code 31 describes a circuit, not a part
The pressure switch on a condensing furnace is a referee. It closes only when the draft inducer has established enough negative pressure to move combustion air safely, and the control will not open the gas valve for high heat until it sees that closed signal. Status code 31 means the signal was absent when the control asked for it, or it went away during the cycle. That is a statement about the whole proving path: the inducer, the vent and intake, the condensate route, the sensing hose, the switch, and the wiring between them.
Reading 31 as a bad switch is the wrong shortcut. A switch that never closes because the vent is packed with snow, or a switch that opens because a condensate trap is full and back-pressuring the inducer, is doing exactly what it should. Replacing it changes nothing. The board is asking for the path to be proven, in order, before any part is named.
What an owner can check, and where it stops
The owner-safe work is on the outside and on the air path. With the furnace off, look at the outdoor vent and intake pipes for frost, ice, snow, leaves, or a blocked screen, and clear anything obvious without dismantling. Check that the furnace filter is clean and that supply and return grilles inside the house are open, because poor airflow can push the furnace toward a limit trip that shows up alongside pressure faults. Confirm the furnace door is fully closed, since the door switch has to be made for the sequence to run.
Everything past that point is technician work. Measuring inducer pressure with a manometer, checking the switch against its rated setpoint, inspecting the condensate trap and drain, testing the inducer motor, and reading wiring continuity all mean opening the furnace with power management and combustion knowledge. Do not bypass the pressure switch to force the furnace to run, because that removes proof that the flue is clear.
What to give the technician
Give the technician the Carrier furnace model, the exact status code and any codes shown with it, whether 31 tracks with cold weather or wind, whether it repeats fast from every start, and whether any venting or control work was done recently.
Safe homeowner checks
- With the furnace off, clear any frost, ice, snow, or debris from the outdoor vent and intake terminations and confirm the terminations are not obstructed.
- Check the furnace filter is clean, the return and supply grilles are open, and the furnace access door is fully closed.
Is a reset appropriate?
A single power cycle to clear the code is reasonable after checking the terminations and filter. If status code 31 returns on the next call for high heat, leave the furnace off for service.
When to call a technician
- Measuring inducer pressure, testing the switch and inducer, clearing the condensate trap, and any wiring or gas-valve work require a qualified heating technician, and the pressure switch must never be bypassed.
Questions people ask about this
Does Carrier status code 31 mean the pressure switch is bad?
Not on its own. Code 31 means the high-heat pressure switch circuit was open when the control needed it closed. A blocked vent, full condensate trap, weak inducer, or wiring fault produce the same code.
Why does status code 31 only happen when it is very cold?
Cold and wind can restrict the vent termination with frost or ice, or push against the outlet, so the inducer cannot build the pressure the high-heat switch needs. The switch then stays open and the board flashes 31.
Can I bypass the pressure switch to get heat?
No. The switch proves the flue path is clear before the burners light. Jumping it removes that safety check and can allow ignition when venting is blocked. It is never an owner step.
Evidence recordHow this page was checked
service manual · checked 2026-09-09
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Carrier technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual
- Scope of the definition
- Carrier two-stage and variable-speed modulating condensing furnaces that report status code 31
- Last checked
- 2026-09-09