Bosch Furnace Error Codes and Troubleshooting Guide

Bosch furnaces use a range of diagnostic signals to report faults, from LED blink sequences to numeric error codes on control boards. This guide explains how to interpret Bosch furnace error codes, common fault categories, basic troubleshooting steps, safety precautions, and when to call a licensed HVAC technician.

Symptom	Common Code Type	Likely Cause	Quick Action
Burner fails to light	Ignition/Flame Failure	Igniter, flame sensor, gas supply, or control issue	Check gas, reset; call tech if persists
Short cycling or lockout	High Limit/Overheat	Restricted airflow, dirty filter, faulty limit switch	Replace filter, inspect vents
Blower won’t run	Blower/Control Fault	Capacitor, motor, or control board problem	Power cycle, call pro
Pressure switch errors	Vent/Pressure Fault	Blocked vent, inducer motor, hose leak	Inspect venting; service required

How Bosch Furnaces Communicate Faults

Bosch furnaces typically use two main diagnostic methods: LED blink patterns on the control board and numeric or alphanumeric error codes displayed on integrated interfaces or remote controllers.

LED blink patterns convey a category and severity of the fault. Numeric codes provide more specific information for technicians and are often found in manuals or service interfaces.

Common Error Code Categories And What They Mean

Understanding the category helps prioritize safety and troubleshooting. Common categories include Ignition and Flame Detection, Pressure and Venting, Limit and Overheat, Blower and Fan, Gas Valve and Supply, Sensor and Thermostat Communication.

Ignition And Flame Detection Errors

These errors indicate the burner does not light or the flame is not detected after ignition. Causes include a failed igniter, dirty flame sensor, faulty gas valve, or disrupted gas supply.

Typical user actions: ensure the gas valve to the furnace is open, inspect for obvious gas leaks (do not operate if a leak is suspected), and reset the furnace per the manufacturer instructions. Persistent failures require a qualified technician to test igniter resistance, flame sensor condition, and control board signals.

Pressure Switch And Venting Faults

Pressure switch errors occur when the inducer motor and venting system do not produce the expected draft. Causes include clogged venting, collapsed or disconnected hose, or a failing inducer motor.

Users should inspect outdoor vent termination for obstructions, clear away debris, and confirm that condensate drains are flowing. Do not attempt inducer motor repair; a technician should test pressure switch continuity and inducer performance.

Limit Switch And Overheat Conditions

Limit or overheat codes appear when the heat exchanger or plenum exceeds safe temperatures. This is commonly caused by restricted airflow from dirty filters, closed supply registers, blocked return grilles, or a failing blower motor.

Immediate steps include replacing or cleaning the air filter and checking vents. Continued lockouts should be addressed by a pro to inspect switch operation and confirm the blower delivers proper airflow.

Blower, Fan, And Electrical Faults

Blower-related error codes point to motor failure, bad capacitors, wiring issues, or control board faults. Symptoms include the blower not starting, running intermittently, or running at incorrect speeds.

Basic checks include verifying power to the furnace, ensuring the thermostat fan setting is correct, and confirming the blower door is properly seated—some models prevent operation if the door is open. Electrical component testing should be done by a technician to avoid shock risk.

Gas Valve And Supply Failures

When the control signals open the gas valve but no gas reaches the burner, or when the valve fails to actuate, the furnace will error. Causes include closed utility gas valve, issues with the gas meter, defective valve, or control board malfunction.

Users should verify the home’s gas valve is open and other gas appliances function. If the gas supply is confirmed but the furnace still reports a valve fault, service is required to test valve operation and control circuits.

Sensors, Thermostat, And Communication Errors

Sensors such as the flame sensor, limit sensors, or temperature probes can fail or drift out of calibration. Communication faults can occur between the thermostat and furnace control board, especially with newer modulating systems.

Resetting the thermostat and verifying wiring connections can resolve some issues. For persistent code indications, a technician will test sensor resistances and replace faulty components as needed.

How To Read LED Blink Codes And Control Board Messages

Consult the specific Bosch furnace manual for the exact LED blink-to-code mapping. Generally, the pattern will show a repeating blink sequence where one pattern indicates the fault category and another the subcode.

When a numeric or alphanumeric code appears on a display, record it exactly. Accurate copying of the code is crucial for technicians and when searching manufacturer resources for fault definitions and recommended repairs.

Basic Safe Troubleshooting Steps For Homeowners

These are actionable steps that preserve safety while resolving common non-technical causes of faults.

• Power Cycle: Turn the furnace off for at least 30 seconds, then restore power to clear temporary faults.
• Check Filter: Replace or clean the air filter if dirty; restricted airflow causes many limit and short-cycling errors.
• Inspect Vents: Ensure supply registers and returns are open and unobstructed; check the outdoor vent cap for blockages.
• Verify Gas Supply: Confirm the home gas shutoff is open and other gas appliances work.
• Thermostat Settings: Confirm thermostat is set to heat and fan settings are correct; replace batteries if wireless.

When To Reset The Furnace

Occasional faults can clear with a reset. Use the furnace reset button or power cycle at the breaker per Bosch recommendations. Limit resets after an overheat condition should only be performed after ensuring proper airflow and resolving the underlying cause.

Repeated resets without addressing the root cause may cause further damage or unsafe operation; call a professional if resets are frequent.

When To Call A Licensed HVAC Technician

Call a certified technician immediately if a code indicates potential gas leaks, persistent ignition failure, pressure switch faults, inducer motor issues, or if the furnace emits unusual odors, soot, or yellow pilot flames.

Qualified service is required for component replacement, gas valve work, control board diagnostics, and any task involving live electrical connections or combustion adjustments.

How Technicians Diagnose Bosch Furnace Codes

Technicians use the recorded code to focus diagnostics: they test sensors with multimeters, measure gas pressure, observe ignition and flame signals with a manometer or scope, and inspect vent pressures and inducer motor amperage.

Advanced Bosch systems may include service menus and log histories; professionals use manufacturer resources and software updates to interpret codes accurately and verify firmware-related issues.

Maintenance Practices To Reduce Error Code Frequency

Proactive maintenance reduces diagnostic events. Recommended practices include scheduled annual service, seasonal filter replacement, annual inspection of venting and condensate drains, and cleaning flame sensors and burners.

Documenting service actions and any recurring codes helps technicians identify intermittent faults and trend failures before they lead to system lockouts.

Safety Precautions And Regulatory Notes

Never attempt to service gas valves, burners, heat exchangers, or high-voltage components unless fully qualified. Improper repairs risk carbon monoxide release, fire, or explosion.

Follow local codes for burner adjustments and combustion testing. Carbon monoxide detectors should be installed and maintained in homes with gas furnaces.

Resources And Manufacturer Support

For accurate code definitions, always consult the furnace’s owner manual and Bosch technical literature specific to the model number. Bosch support and authorized service centers provide model-specific troubleshooting charts and parts references.

Keep the furnace model and serial number accessible when contacting support. This allows faster identification of control board revisions and service bulletins related to known faults.

Key Takeaways And Best Practices

Record codes exactly and avoid repeated resets without inspection. Perform basic safe checks—power cycle, filters, vents, and gas supply—before calling for professional service.

Schedule annual preventive maintenance with a licensed technician to minimize unexpected failures and ensure combustion safety and system efficiency.

Action	When To Do It
Replace Air Filter	Every 1–3 Months
Clean Flame Sensor/Burners	Annual Service
Inspect Venting	Seasonally Or If Pressure Errors Occur
Record Error Codes	At Every Fault Event

If a specific Bosch furnace error code is available from the user, include that code when seeking support to receive the most accurate troubleshooting steps and safety advice.