Understanding Common Furnace Error Codes

Modern furnaces communicate problems through error codes displayed on the thermostat, the furnace control board LED, or a digital readout panel. Understanding what these codes mean can help you determine the urgency of a problem and whether it is related to your inducer motor. Here is a practical guide.

How to Read Furnace Error Codes

Error codes vary by manufacturer, but they are typically displayed as blinking LED patterns on the furnace control board, numerical codes on smart thermostats like Ecobee or Nest, or alphanumeric codes on communicating furnace systems. Check your furnace manual for the specific code meanings for your brand and model.

Pressure Switch Fault — The Most Common Inducer-Related Code

A pressure switch fault code (displayed variously as 'Pressure Switch Open', 'PS Fault', or specific blink codes) is the most frequently encountered error code related to the inducer motor. The pressure switch monitors airflow created by the inducer. Possible causes include:

• Inducer motor failure — motor not spinning or spinning too slowly
• Blocked or cracked pressure switch hose
• Blocked flue or vent pipe
• Failed pressure switch (the switch itself, not the motor)
• Condensate drain blockage on high-efficiency furnaces
• Blocked inducer fan wheel (carbon deposits or debris)

Inducer Motor Fault Codes

Some higher-end furnaces with communicating controls will display a specific inducer motor fault code. This typically indicates the control board has detected that the motor is drawing incorrect amperage, running at the wrong speed, or has failed to start within the required time window. This code almost always requires professional service.

Flame Sensor and Ignition Failure Codes

While not directly related to the inducer motor, ignition failure codes often occur as a secondary symptom of inducer problems. If the inducer is not creating proper draft, the pressure switch will not close, and the furnace will display an ignition lockout code even though the igniter itself is fine. Always diagnose inducer operation first when troubleshooting ignition failures.

Limit Switch Codes

High-limit switch trips can also be related to inducer issues. If the inducer is running but airflow is restricted, heat can build up in the heat exchanger and trigger the high-limit switch as a safety measure. Common causes include dirty filters, blocked vents, or a partially failing inducer motor.

When to Call vs. When to DIY

• DIY safe: Replace furnace filter, check and clear blocked exterior vents, reset furnace after a power outage
• Call a professional: Pressure switch faults (diagnosis required), inducer motor codes, heat exchanger or limit switch faults, any carbon monoxide alarm situation
• Emergency call: Carbon monoxide alarm triggered, smell of gas, complete furnace failure in extreme cold

If your furnace is displaying any error code related to the inducer motor or pressure switch, our certified technicians at ROMA Heating & Cooling can diagnose and repair the issue quickly. We serve all of Metro Vancouver with same-day service. Call 778-909-5731 — available 24/7 for emergencies.