Bryant Furnace Blink Codes: 3, 4, 7, 13 Flashes — 915S, 925S, 987M Diagnosis

Common Symptoms

• Control board LED blinking a repeated counted flash pattern
• Furnace not heating or short-cycling on limit
• Furnace ignites briefly then shuts off multiple times before going silent
• Blower running continuously but no heat output
• Furnace completely locked out — manual reset required to restart
• 13-blink code displayed after furnace ran for several minutes then stopped

Most Likely Causes

1. 1

   3 Blinks — Pressure Switch Fault

   The draft inducer ran but the HK42FZ board did not see the pressure switch close within the required window. Causes: a kinked or condensate-blocked pressure hose, an inducer motor not building adequate draft (failing capacitor, dirty housing, cracked wheel), a blocked flue or condensate drain on 90+ efficiency Bryant models (987M, 926T), or a defective pressure switch HH18HA499. Bryant and Carrier use the same pressure switch assembly — HH18HA499 is the common Bryant/Carrier replacement switch. The HK42FZ board also monitors for pressure switch stuck closed — on some Bryant boards, a 3-blink code can indicate either stuck open or stuck closed depending on timing; read the fault code carefully in context of when the fault occurs (before or after inducer start).

2. 2

   4 Blinks — Open High-Limit Device

   The high-limit switch has opened — the heat exchanger is overheating. Primary cause: clogged air filter. Secondary causes: blocked return air, closed supply registers, or a blower motor running below rated speed. On Bryant 915S models with a PSC blower motor, a weak run capacitor is a common cause of repeated 4-blink codes. The capacitor reduces the blower RPM over time, reducing airflow below the minimum needed to keep the heat exchanger cool. This generates 4-blink codes even with a clean filter because the blower simply is not moving enough air.

3. 3

   7 Blinks — Gas Valve / Ignition Lockout

   The furnace attempted ignition but failed to establish or prove a stable flame, and locked out. On Bryant/Carrier boards, the 7-blink code specifically indicates a gas valve circuit fault or ignition lockout from the gas valve side — the board commanded the gas valve open but did not detect a flame within the trial period. Causes: gas valve coil failed (test resistance across valve terminals — 20–60 ohms healthy, OL means failed), gas valve mechanically stuck closed, inadequate gas pressure at the manifold, or the igniter failed to reach full temperature before the gas valve opened (causing a cold-start misfire). Check gas pressure at the manifold with a manometer during a heat call if valve and igniter both test good.

4. 4

   13 Blinks — Limit Device Lockout (3 Consecutive Trips)

   The high-limit switch tripped three times in a single demand cycle and the Bryant HK42FZ board entered hard limit lockout. This is the critical Bryant/Carrier-specific code — 13 blinks means the board is done attempting to recover from limit trips and will not start ignition again until manually reset. The underlying cause is significant airflow restriction causing sustained overheating. Unlike a single 4-blink limit trip that may be caused by a dirty filter alone, 13-blink lockout means the furnace has been trying to heat three times, overheating every time. Causes: severely clogged filter, completely blocked return air duct, failed blower motor not moving air at all, failed KGASF00D4 inducer motor, or an undersized duct system for the furnace capacity.

5. 5

   8 Blinks — Inducer / Pressure Fault

   The inducer motor KGASF00D4 did not start or the pressure switch signal indicates an inducer problem — not a pressure switch or hose fault. Causes: the inducer motor itself has failed (bearing seized, motor winding open), the inducer capacitor has failed (measure capacitance, should be within 10% of rated µF), or the inducer wheel is so badly fouled with debris that the motor cannot spin up. On Bryant 925S and 987M models, the inducer motor KGASF00D4 is a known service item after 10 years of operation.

Quick DIY Checks

1. 1Count the blink code and locate the board: open the lower access panel on the Bryant furnace to see the HK42FZ or HK61EA control board. The status LED is on the board face — count the flashes before the pause. Bryant blink codes: 3 blinks (pressure switch), 4 blinks (open limit), 5 blinks (flame sensed without call — check gas valve), 6 blinks (115V reversed), 7 blinks (gas valve/ignition lockout), 8 blinks (inducer/pressure fault), 13 blinks (limit lockout). The 13-blink code is distinctive — you will count thirteen distinct flashes before the pause. This code does not repeat the same as 3 flashes x4+1; it is a true 13-count sequence. On Bryant furnaces with a Côr thermostat or Evolution system, fault codes also display on the thermostat screen — navigate to the diagnostics menu.
2. 2For 13-blink limit lockout — the most urgent diagnosis: this code means the limit has opened three times. Before resetting: (1) Replace the air filter — even if it looks new, a heavily loaded filter is the most common cause. (2) Walk through every supply register in the home and open any that are closed or partially closed — at minimum 80% of registers must be open. (3) Check the return air grille for blockage — a return covered by furniture or drapes will starve the furnace of air even with a clean filter. (4) Listen for the blower motor: with a heat call, the blower should start within 45–60 seconds of the burners lighting. If the blower does not start or starts very slowly, suspect the run capacitor or motor on older Bryant 915S and 925S units. (5) Only after addressing airflow: cycle the furnace power off for 30 seconds and back on to clear the 13-blink lockout.
3. 3For 7-blink gas valve/ignition lockout: power cycle the furnace and observe the startup sequence through the sight glass. You are watching for (1) inducer start, (2) igniter glow (orange-white glow visible approximately 40 seconds into startup), (3) gas valve opening and flame lighting. If the igniter glows brightly but no flame appears: verify the main gas shutoff valve is fully open (handle parallel to the gas pipe = open; perpendicular = closed). Test gas valve coil resistance — on Bryant/Carrier furnaces the gas valve shares design with the Carrier platform. Disconnect the coil wires and test resistance: main valve operator coil typically reads 20–60 ohms. If the igniter does not glow at all: test the hot surface igniter (Bryant uses the same igniters as Carrier — LH33ZS004 and compatible alternatives). OL on the ohmmeter means cracked, needs replacement.

1. 4For 3-blink pressure switch fault: locate the HH18HA499 pressure switch — typically mounted on the cabinet wall near the inducer housing, connected by a small rubber hose and a wire connector. Trace the pressure hose for kinks and condensate buildup. Disconnect both ends and blow through the tube to clear it. On 90+ efficiency Bryant models (926T, 987M), also find the condensate trap at the base of the secondary heat exchanger and verify it is draining freely — a clogged Bryant condensate trap is the most common source of 3-blink codes on high-efficiency units after the hose is confirmed clear. Test the pressure switch HH18HA499 by applying gentle suction to the hose port with the switch disconnected from the hose — contacts should click closed with suction.
2. 5For 8-blink inducer/pressure fault: with power on and a heat call active, listen for the inducer motor KGASF00D4 to start within 30 seconds. If you hear nothing, check the inducer motor: turn off power, remove the lower panel, and try to spin the inducer wheel by hand through the housing — it should spin freely with no grinding. If it spins freely, the issue is likely the inducer motor capacitor. Test capacitor capacitance (most Bryant inducer capacitors are 3–7 µF) — a reading more than 10% below rated value means the capacitor has failed and the motor cannot start under load. If the wheel does not spin freely, the motor bearings have failed and the entire inducer assembly KGASF00D4 needs replacement.
3. 6Lockout reset for Bryant: set thermostat to OFF. Flip the furnace power switch to OFF and wait 30 full seconds. Restore the power switch, then set the thermostat to HEAT at least 5°F above room temperature. For 13-blink limit lockout, ensure all airflow corrections (filter, registers, blower check) have been completed before resetting — the board will re-enter 13-blink lockout within one heat cycle if the airflow problem is not corrected. For 7-blink ignition lockout, confirm igniter, flame sensor, and gas supply have been verified before resetting. Bryant furnaces with Côr thermostats may also require clearing the fault code from the thermostat diagnostics menu.

Repair vs Replace

Recommended Tools & Parts

• Bryant Carrier Hot Surface Igniter (LH33ZS004 compatible)

  Replacement hot surface igniter for Bryant 915S, 925S, 987M, 926T, and 310AAV furnaces. Same part as Carrier — fixes 7-blink gas valve/ignition lockout caused by a cracked igniter. Common Bryant/Carrier igniter part numbers include LH33ZS004, LH33ZS002, and KGAPK0101AAA. Verify voltage (120V) before ordering.

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• Bryant Carrier Pressure Switch (HH18HA499)

  Replacement inducer pressure switch for Bryant furnaces — fixes 3-blink pressure switch fault and 8-blink inducer/pressure faults when hose is clear. HH18HA499 covers the majority of Bryant and Carrier furnace models. Verify the water column (WC) rating matches your existing switch.

  $25–$60

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• Bryant Furnace Control Board (HK42FZ011)

  Replacement OEM control board for Bryant furnaces — fixes persistent blink codes after all components have tested good. HK42FZ011 is the most common Bryant/Carrier control board. Identical to the corresponding Carrier board. Verify board number against the label on your existing board before ordering.

  $80–$160

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• Bryant Inducer Motor Assembly (KGASF00D4)

  Replacement draft inducer motor assembly for Bryant 925S, 987M, 926T furnaces. Fixes 8-blink inducer/pressure fault caused by a failed inducer motor after capacitor has been ruled out. Includes motor and housing assembly — verify model number compatibility before ordering.

  $150–$300

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Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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