Bryant Furnace Pressure Switch Codes (23, 31, 32): Meaning & Fixes

Bryant's pressure switches are the furnace's proof that its exhaust has somewhere to go: no proven draft, no ignition. Four codes report on them — 23 (a switch did not open before the cycle), 31 (the high-heat switch did not close or reopened), 32 (the low-heat switch did not close or reopened) and 43 (the low-heat switch open while the high-heat switch is closed, the subtlest report on the Bryant chart). This article gives each code its own section from Bryant's manuals, then the shared causes — venting, inducer, condensate, wind — and the safety rule Bryant's literature never bends: a pressure switch is never jumpered, adjusted or bypassed to get heat.

What the pressure switches prove — and the order Bryant checks them in

On a Bryant two-stage or variable-speed furnace there are two pressure switches, a low-heat switch (LPS) and a high-heat switch (HPS), each connected by a small tube to the inducer/vent side of the furnace, and the control interrogates them in a strict order that explains all four codes in this article. The interrogation starts before anything moves: when the thermostat calls for heat, the control's self-check verifies that both switches are OPEN. A switch that is already closed at that moment has failed the first question — that is code 23, and the cycle does not begin. Then the inducer motor starts and slowly increases speed, pulling exhaust through the heat exchanger and vent. The low-heat switch must close first: on the variable-speed control, the moment it closes, the control notes the inducer RPM, treats it as a measurement of the vent system's resistance, and starts the 25-second prepurge. If the cycle is a high-heat cycle, the control keeps raising inducer speed until the high-heat switch also closes, notes that RPM too, and runs prepurge from there. Only with the proving switches closed does the sequence move on to the igniter and gas valve. Single-stage Bryant furnaces run the same logic with one switch and one speed — their labels print a single did-not-close code (31) where the two-stage boards split it into 31 for high-heat and 32 for low-heat. Two design facts follow from this architecture. First, the switches are proven in both directions every cycle: open when they must be open, closed when they must be closed — which is why 'did not open' and 'did not close' are separate codes with separate suspects. Second, the switches are measuring the vent, not themselves: a switch that will not close is usually reporting a vent path, an inducer or a condensate problem honestly, and Bryant's cause lists for these codes are vent lists first and switch lists last.

Code 23: pressure switch did not open

Bryant's definition is consistent across every document checked: check for an obstructed pressure tubing, or a pressure switch stuck closed. The variable-speed guide sharpens the timing: the status code indicates the low-heat or high-heat pressure switch is MADE (closed) when a call for heat is initiated, and the control will flash 23 until the switch opens — then the cycle begins. So a furnace sitting at 23 has not failed to start its inducer; it has refused to, because its vent-proof device is claiming draft exists when nothing is running. Two physical stories produce that claim. The tubing story: the small hose between the switch and its pressure port is obstructed — kinked, water-logged, or blocked at the port — trapping pressure on the switch side so the contacts never release even though the vent is at rest. The switch story: the contacts themselves have stuck or welded closed, and the switch reports 'closed' as a permanent condition. Bryant's troubleshooting flow for 23 works through the wiring and both switches methodically and ends, on the evidence, at replacing the pressure switch assembly — and in one branch (the inducer running when it should not be) at the inducer or the control. For the owner, the safe observations are these: 23 present before any inducer sound is normal-sequence behaviour for this code, not a broken inducer; and a 23 that clears after the furnace sits (trapped pressure bleeding off through a partly obstructed tube) is still a fault that will return. What 23 must never provoke is the jumper wire: a switch that cannot be trusted to open cannot be trusted to prove the vent closed either, and firing on a defeated switch removes the furnace's only evidence that its exhaust path is clear.

Code 31: high-heat pressure switch did not close or reopened

On two-stage and variable-speed Bryant boards, 31 is the high-heat switch's report: the 355MAV guide defines it as the high-heat pressure switch input failing to close on a call for high-heat, or opening during high-heat — and adds two suspects the standard lists bury: the control relay may be defective, or the gas valve is mis-wired. (On single-stage Bryant labels, the same code number 31 is printed without the high-heat qualifier — it is simply 'pressure switch did not close or reopened' for the furnace's one switch; the behaviour and timing that follow are the same.) The control's patience is timed and documented: if the switch stays open longer than 5 minutes, the inducer shuts off for 15 minutes before retry; and if the switch REOPENS during the blower on-delay period, the blower will come on for the selected blower off-delay. Bryant's check list for the closing failure is the vent-path census: proper vent sizing; a restricted vent; disconnected or obstructed pressure tubing; a defective inducer motor; low inducer voltage (115V); inadequate combustion air supply; excessive wind; a defective pressure switch; and low inlet gas pressure where a low-gas-pressure switch (LGPS) is fitted. Read as a system, the list walks the draft backwards from the vent termination (sizing, restriction, wind) through the machine that makes the draft (inducer motor and its voltage) to the tube that carries the signal and the switch that reads it. High-heat specificity matters in the field pattern: a furnace that runs low fire happily and faults only when high-heat calls is failing the harder test — more inducer speed, more vent flow, a second switch to satisfy — and the suspects narrow to whatever is marginal at full draft: a partly restricted vent, a tiring inducer, or the high switch itself.

Code 32: low-heat pressure switch did not close or reopened

Code 32 is the low-heat switch's version of the same report: the input failed to close on a call for low-heat, or opened during low-heat. The label wording also folds in the draft safeguard or aux-limit switch where those are used (the 330JAV label marks the aux-limit branch downflow-only), because on those models the proving chain shares the code. Bryant builds two behaviours around 32 that its sibling code does not have, and both are diagnostic gold. If the switch opens during the blower on-delay period, the blower comes on for the selected blower off-delay — a small courtesy run. But if the low-heat switch opens WITHIN 5 MINUTES AFTER IGNITION, the next heating cycle will be restricted to high-heat: the control, having lost low-fire draft mid-run, stops offering low fire until it has seen a clean cycle, pushing the furnace onto the stronger draft of high-heat where the proving is easier to hold. Owners experience this as a furnace that suddenly only runs on its loud, high setting — it is code 32's documented consequence, not a new fault. The cause list adds the condensing-furnace branch that the 31 lists underplay: alongside the shared vent census (proper vent sizing, excessive wind, restricted combustion air supply, disconnected or obstructed tubing, improper pressure-switch wiring, low inlet gas pressure where LGPS is used), Bryant lists for 32 a PLUGGED CONDENSATE DRAIN and WATER IN THE VENT PIPING, with a sagging pipe as the named suspect — on a condensing Bryant (the Preferred and Evolution high-efficiency lines), water standing in the vent or backing up from a blocked trap changes the pressure the low switch sees, and low fire, with the gentlest draft of the cycle, is where that marginal pressure fails first. A 32 on a condensing furnace therefore starts at the condensate trap and the vent's slope, before it starts at the switch.

Code 43: low-heat switch open while the high-heat switch is closed — the subtle one

Code 43 is the Bryant chart's logic puzzle, and it deserves slow reading, because its definition contains its own diagnosis. The high-heat pressure switch requires MORE draft to close than the low-heat switch does — high fire moves more exhaust, and its switch is set accordingly. So consider what 43 reports: the high-heat switch is CLOSED (draft strong enough for the harder test has been proven) while the low-heat switch is OPEN (claiming even the easier test failed). Both switches breathe the same vent through similar tubes. If the vent were truly restricted, the high switch would be the first to fail, not the last to succeed — so a 43 cannot be read as 'weak draft' without contradicting the furnace's own evidence. Bryant's check list for 43 follows that logic exactly, and it is a switch-side list, not a vent list: a low-heat pressure switch stuck open; disconnected or obstructed pressure tubing (the low switch's own tube, which can be blocked, split or off its port while its sibling's tube is fine); improper pressure-switch wiring; a plugged condensate drain; water in the vent piping, with a sagging pipe named; and low inlet gas pressure where a low-gas-pressure switch is used. In other words, 43 accuses the low-heat switch, its tube or its wiring — the vent itself has an alibi, provided by the closed high-heat switch. This is also where a common internet shorthand goes wrong: third-party lists call 43 a 'pressure switch calibration fault', but Bryant's own definition is the open-while-closed report above ('out-of-calibration pressure switches' appear in Bryant's documents only as one listed cause under code 32). A technician answering a 43 starts at the low switch with a manometer — measuring the actual pressure at the switch against its rating — and at its tube and wiring, and only replaces the switch when measured draft at that port exceeds the switch's setpoint while the contacts stay open. Guessing at vent work for a 43 spends money on the one part of the system the code has already cleared.

Shared causes: venting, inducer, condensate and wind

Codes 31, 32 and (at one remove) 23 fail on the same physical chain, and Bryant's lists across the three codes name every link. The vent path itself: a restricted vent — bird or insect nests at the termination, ice or snow over the pipes in a cold snap, a crushed or poorly jointed run; improper vent sizing, where an over-long or under-diameter run never develops the pressure the switches need; and water in the vent piping where a sagging horizontal run pools condensate in the pipe's belly (Bryant names the sag explicitly). The machine that makes the draft: the inducer motor — worn, seized, or under-fed, with Bryant listing low inducer voltage — and, on the variable-speed control, the inducer's reported RPM, which the control itself uses to judge vent resistance at the start of every cycle. The water system, on condensing models: a plugged condensate drain or trap backs water toward the collector box and vent, which is why Bryant puts the plugged drain on the 32 and 43 lists — clearing the outdoor terminations while forgetting the trap is the classic half-fix. The signal path: pressure tubing disconnected, obstructed, cracked or water-filled, and pressure-switch wiring — cheap links that imitate expensive ones. The weather: excessive wind appears on every Bryant list for these codes, because wind pressure at a termination can hold a switch open or blow it open mid-cycle; a furnace whose 31/32s correlate with windy nights is reporting its termination placement, not its switch. And the switches themselves, last by Bryant's ordering on every list: a switch is condemned on measurement — draft proven above its setpoint with the contacts in the wrong state — never on suspicion. The owner-safe portion of this chain is real but bounded: clear the outdoor intake and exhaust terminations, and check the condensate drain on a condensing model. Everything inside the cabinet is technician work.

Never jumper the switch: the safety logic Bryant builds around these codes

Every code in this article exists because the furnace refuses to fire until it has proven its exhaust can leave the building — and the failure mode the proof guards against is the one that makes furnaces lethal: combustion gases, including carbon monoxide, spilling into the home instead of travelling up a blocked or failed vent. That is why the control checks the switches in both directions (a switch stuck closed, code 23, blocks the cycle just as firmly as one that will not close), why a switch that drops out mid-run shuts the gas valve down, and why Bryant's retry behaviour is patient but bounded — a 15-minute inducer rest after 5 open minutes, a next cycle restricted to high-heat after a low-fire dropout — rather than an endless hammering at a vent that will not prove. Jumpering a pressure switch, or 'adjusting' one to make a furnace run, deletes the only witness the system has. A furnace that then fires into a restricted vent does not announce the danger in any way a household can sense: carbon monoxide is colourless and odourless, which is why Bryant's manuals treat the pressure switches as safety controls in the same class as the limit and rollout switches, and why every fix path in this article ends at restoring the vent, the inducer, the drain or the switch — never at defeating the messenger. If a Bryant furnace will not prove draft, it is not being stubborn; it is being the last working part of the safety system. Use backup heat, clear the terminations and the condensate trap, and let a technician measure the draft. The switch is cheap. What it stands in for is not.

Key takeaways

• Read the stage before the code: 23 happens before the inducer runs, 31/32 happen while it is proving or holding draft, and 43 is a disagreement between the two switches. The stage halves the suspect list before anyone opens a panel.
• On a condensing Bryant (Preferred/Evolution high-efficiency models), add the condensate trap and drain to your first checks for 31/32/43 — Bryant lists a plugged condensate drain on these codes, and it imitates a failing switch.
• Note the weather with the code: pressure-switch faults that arrive on windy nights or in snow point at the vent terminations and their placement, and that note is worth money to the technician who follows it up.

Resetting the Bryant furnace

Bryant's lockouts run on documented timers, and they are not interchangeable. Limit lockout (13) and ignition lockout (14) auto-reset after 3 hours. Blower motor lockout (15, variable-speed boards) also auto-resets after 3 hours. Control circuitry lockout (45) auto-resets after 1 hour, and Bryant adds: reset power to clear the lockout — if 45 repeats, replace the control. Gas heating lockout (21) is the exception with NO auto-reset: Bryant's instruction is to turn off power and wait 5 minutes to retry. The pressure-switch behaviour under 31/32 (inducer shuts off for 15 minutes after the switch has been open 5 minutes, then retries) is a retry pause, not a lockout. Everything else on the Bryant chart is a condition code that clears when its condition clears: 33 ends when the limit or rollout switch remakes as the furnace cools (the rollout switch itself is manual-reset hardware — no timer resets it, and Bryant requires its cause to be corrected before it is reset), and 24 ends only when the 24-volt short is repaired and the fuse replaced. Interrupting power restarts a Bryant control, but on the older boards it also erases the stored fault history — read the history first, and never treat a cleared timer as a repaired furnace: an unfixed cause simply walks the control back into the same lockout.

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Facts on this page were checked against manufacturer documentation: shoredist.com · manuzoid.com · www.manualshelf.com · www.manualsdir.com · www.manualshelf.com · manualsdump.com · manualsdump.com · www.manualsdir.com · www.manualslib.com · manuals.plus