How To Reset Furnace Ignitor: A Complete Troubleshooting And Replacement Guide
While modern gas furnaces do not feature a physical reset button specifically for the ignitor, resetting the entire heating system safely clears lockouts, resets the control board, and re-initiates the ignition sequence. This comprehensive guide outlines the exact diagnostic and reset protocols required to restore your furnace safely and efficiently.
Pre-Operation and Safety Equipment Checklist
Troubleshooting a modern gas furnace requires a methodical approach to safety, electrical hazards, and combustion controls. Before touching any internal components, you must ensure you have the correct tools and understand the operational threshold of your specific heating appliance. Most residential forced-air furnaces operate on 120V AC electrical power and utilize either a Silicon Carbide or Silicon Nitride hot surface ignitor operating at roughly 12V to 24V from the integrated furnace control board, or direct spark ignition variants.
Essential Gear, Tools, and Materials:
- Digital Multimeter (capable of measuring AC/DC voltage and ohms/continuity)
- 1/4-inch nut driver or screwdriver set
- Isopropyl alcohol (99%) and a clean microfiber cloth for cleaning flame sensors
- Work gloves and safety glasses
- Flashlight or headlamp
Mandatory Prerequisite Knowledge and Standards:
- Familiarity with turning off main electrical service via the wall switch or breaker.
- Understanding of natural gas or propane shut-off valve locations.
- Compliance with local mechanical and National Fuel Gas Codes (NFPA 54) regarding appliance servicing.
Estimated Budget and Duration Benchmarks:
- Time required: 15 to 45 minutes for a standard diagnostic and reset procedure.
- Cost: Free for a basic power reset or flame sensor cleaning; $20 to $60 if a replacement ignitor is required.
Step-by-Step Furnace Reset and Ignitor Troubleshooting Workflow
Step 1: Locate the Thermostat and Lower the Temperature Setting
Before altering the power supply to the appliance, walk to your wall-mounted thermostat and adjust the mode from "Heat" to "Off," or lower the set temperature at least five degrees below the current room temperature. This prevents the control board from attempting a call for heat while you are performing diagnostic checks, ensuring the system remains in a safe standby state.
Step 2: Cut Power to the Furnace
Locate the furnace service switch, which typically resembles a standard light switch mounted directly on the side of the furnace chassis, on a nearby wall, or inside the utility closet. Flip this switch to the "Off" position. If your system lacks a dedicated service switch, locate your main electrical service panel (circuit breaker box) and switch off the breaker dedicated to the HVAC system to completely isolate the 120V power supply.
Step 3: Perform a Hard Power Reset
Leave the electrical power disconnected for a minimum of 60 seconds. This duration allows the capacitors on the integrated furnace control board to fully discharge, clearing any temporary fault codes, ignition lockouts, or safety trip histories stored in the temporary memory. After the minute has elapsed, restore power by flipping the service switch or circuit breaker back to the "On" position.
Warning: Never attempt to bypass safety switches, such as the door switch or rollout switch, while troubleshooting ignition issues. Doing so creates an extreme risk of electrical shock, carbon monoxide poisoning, or fire.
Step 4: Observe the Diagnostic LED Code Sequence
Remove the upper and lower service panels of the furnace. Secure the door safety switch (if required by your specific model) by taping it down or depressing it manually, keeping safety in mind. Turn the thermostat back up to initiate a call for heat. Watch the viewing window on the draft inducer motor or the LED light on the integrated control board to observe the startup sequence and note any flashing error codes.
Step 5: Inspect and Test the Ignitor Circuit
Listen for the inducer motor to start, followed by a clicking sound from the pressure switch, and then observe the hot surface ignitor. A healthy silicon nitride or silicon carbide ignitor will begin to glow a bright, blinding orange-white within 30 to 45 seconds of the call for heat. If the ignitor does not glow, use your digital multimeter set to AC volts to test for 120V power at the ignitor plug harness when the control board initiates the heating cycle. If power is present but the ignitor remains cold and dark, the ignitor element has failed and must be replaced.
How to Relight a Pilot Light on Your Furnace | Angi
Furnace Ignitor Types and Technical Specifications Matrix
| Ignitor Type | Operating Voltage | Normal Resistance (Ohms) | Average Lifespan | Common Failure Mode |
|---|---|---|---|---|
| Silicon Carbide (SiC) | 120V AC / 24V AC | 40 to 90 Ohms (cold) | 3 to 5 Years | Micro-cracks, thermal shock, high resistance |
| Silicon Nitride (Si3N4) | 120V AC / 24V AC | 15 to 70 Ohms (cold) | 7 to 10 Years | Structural degradation from sustained over-voltage |
| Direct Spark Ignition | High Voltage (Spark) | N/A (Spark Gap) | 10+ Years | Carbon buildup, electrode misalignment, cracked ceramic insulator |
Common Ignition Failures and Field Fixes
Understanding the root cause of an ignition failure prevents unnecessary part replacements and ensures long-term heating reliability.
Root Cause: Accumulated soot, dust, or oil residue on the flame sensor rod, which prevents the control board from verifying burner ignition and causes the system to shut down after three to four seconds.
- Actionable Fix: Turn off power to the furnace, remove the single mounting screw holding the flame sensor, and gently scrub the metal rod with a fine abrasive pad or 99% isopropyl alcohol until shiny before reinstalling.
Root Cause: Hairline cracks or complete structural fracture of the hot surface ignitor element caused by thermal expansion or accidental contact during previous maintenance.
- Actionable Fix: Inspect the ignitor visually for breaks or white spots. If continuity testing yields an open circuit (infinite ohms), replace the ignitor with an OEM-matched unit without touching the brittle ceramic element with bare skin.
Root Cause: A persistent pressure switch trip preventing the control board from advancing to the ignitor warm-up phase due to a blocked condensate trap, dirty vent pipe, or failing inducer motor.
- Actionable Fix: Clear all PVC intake and exhaust flues of obstructions, inspect rubber pressure switch tubing for cracks, and ensure condensate drain lines flow freely.
Root Cause: Control board lockout due to repeated ignition failures, resulting in a permanent code that requires a physical power interruption to clear.
- Actionable Fix: Perform a hard system reset by cutting power at the service switch for 60 seconds after resolving the underlying gas supply or venting issue.
Frequently Asked Questions
Why does my furnace ignitor glow, but the burners fail to light?
If the ignitor glows brightly but the gas valve does not open, the control board is either failing to send voltage to the gas valve, the gas valve is stuck, or the flame sensor is failing to detect the flame. Verify that your manual gas supply shut-off valve is fully open and test for 24V AC at the gas valve terminals during the ignition trial.
Can I touch a new furnace ignitor with my bare fingers?
No, you should never touch the ceramic or carbide element of a new hot surface ignitor with your bare hands. The natural oils and salts from human skin create hot spots on the surface when energized, leading to premature thermal shock and failure of the component. Always handle the ignitor by its ceramic base or wear clean cotton gloves.
How do I know if my furnace ignitor is completely broken?
A broken ignitor will typically show a visible crack, break, or blistering along the element. If it appears visually intact, use a digital multimeter set to the resistance (ohm) setting to test the terminals; an infinite reading or a reading significantly outside the manufacturer specification indicates an open circuit and a failed part.
What is the difference between a furnace reset button and a hard reset?
Most modern furnaces do not feature a dedicated manual reset button on the control board or ignitor assembly. Instead, a "reset" is performed by cycling the 120V power supply via the external service switch or circuit breaker to clear error codes and restart the microprocessor.
When should I call a professional HVAC technician?
You should call a licensed technician if you smell natural gas, suspect a cracked heat exchanger, experience persistent flame rollout, or if replacing the ignitor and cleaning the flame sensor does not resolve the ignition lockout condition.
Schedule Professional HVAC Maintenance and Repair Services
If your furnace continues to experience lockout cycles or refuses to ignite after performing a system reset, our certified technicians are available to provide comprehensive diagnostic and repair services. Contact us today to schedule your professional heating system inspection and ensure safe, reliable warmth for your home.
