Top 5 Signs Your Furnace Ignitor Needs Replacement

Hot surface ignitors are one of the most critical—and most commonly replaced—components in gas furnaces and heating appliances. While modern silicon nitride ignitors can last 5-10 years or more, they don't last forever. Recognizing the warning signs of impending failure can save you from unexpected downtime, emergency service calls, and uncomfortable customers or tenants.

In this guide, we'll explore the five most reliable indicators that your furnace ignitor is approaching the end of its service life, along with actionable troubleshooting steps and replacement considerations.

Sign #1: Delayed or Intermittent Ignition

What to Look For

The furnace cycles through its startup sequence, the ignitor glows, but ignition doesn't happen immediately. You may hear the gas valve open, followed by a delay of 2-5 seconds before you hear the "whoosh" of ignition—or sometimes no ignition at all, leading to a safety lockout.

Why This Happens

As ignitors age, their electrical resistance increases and their ability to reach and maintain optimal temperature degrades. A weakened ignitor may reach 2,100°F instead of the required 2,500°F, creating marginal ignition conditions:

• On cold days, when gas is denser, ignition may succeed
• On warmer days, with less dense gas mixture, ignition fails
• Humidity and air density variations affect performance
• Each failed attempt further degrades the element

Diagnostic Steps

1. Measure current draw: Compare to manufacturer specifications. A declining current (indicating increased resistance) signals degradation
2. Observe glow pattern: Look for dim spots or non-uniform heating
3. Time the warm-up: If it takes longer than spec (typically 17-30 seconds), the ignitor is weakening
4. Check voltage: Ensure the ignitor receives proper voltage (typically 120V AC)

When to Replace

If you observe delayed ignition more than once, replacement is recommended. Continued operation risks:

• Incomplete combustion and carbon monoxide production
• Gas buildup leading to delayed ignition "puffs"
• Nuisance lockouts requiring manual resets
• Complete failure during peak heating season

Sign #2: Visible Cracks or Physical Damage

What to Look For

During visual inspection, you notice cracks, chips, or breaks in the ceramic element. These may appear as:

• Hairline fractures across the heating element
• Chips or missing pieces at the tip
• Separation between the element and mounting base
• Discoloration patterns indicating thermal stress

Common Causes of Physical Damage

Thermal Shock: Rapid temperature changes—such as when cold air blows directly on a hot ignitor—cause the ceramic to expand and contract unevenly, leading to stress fractures.

Mechanical Impact: Damage during installation, service, or from debris in the air stream can crack the brittle ceramic material.

Improper Handling: Touching the element with bare hands deposits oils that create hot spots during operation, eventually causing cracks.

Vibration: Loose mounting or excessive blower vibration can fatigue the ceramic over time.

Why Cracks Are Critical

Even small cracks create serious problems:

• Electrical arcing: Current may arc across gaps, causing erratic operation
• Propagation: Small cracks grow rapidly with each thermal cycle
• Element failure: The ignitor may break completely, often mid-cycle
• Safety risk: A broken element can fall onto the burner or into the airstream

Prevention Strategies

• Always wear clean gloves when handling ignitors
• Ensure proper mounting with appropriate torque
• Verify adequate clearance from all components
• Check that blower mounting is secure and vibration-free
• Install ignitor guards in high-vibration applications

Sign #3: Increased Warm-Up Time

What to Look For

The ignitor takes noticeably longer to reach full brightness than it did when new. Where it once glowed bright orange-white in 20 seconds, it now takes 35-45 seconds or more.

Understanding the Science

Hot surface ignitors work on the principle of resistive heating. As current flows through the ceramic element, electrical resistance converts electrical energy to heat (P = I²R). As ignitors age:

• Micro-structural changes increase overall resistance
• Higher resistance means lower current draw for same voltage
• Lower current means reduced heating power
• The element takes longer to reach ignition temperature

Measurement Techniques

Baseline Comparison: Record warm-up time and current draw when installing a new ignitor. Check these values during annual maintenance.

Current Draw Test:

1. Using a clamp-on ammeter, measure current during warm-up
2. Compare to manufacturer specifications (typically 3.0-4.5 amps for silicon nitride)
3. A decline of 15-20% indicates significant degradation

Resistance Check:

1. With power OFF, disconnect ignitor leads
2. Measure resistance with a multimeter
3. Compare to spec range (11-70 ohms for most silicon nitride models)
4. Out-of-range readings indicate failure or imminent failure

Performance Impact

Extended warm-up time creates several issues:

• Delayed comfort: Longer wait for heat delivery
• Nuisance lockouts: Control boards have maximum warm-up timeouts
• Increased energy use: Ignitor consumes power longer each cycle
• Wear on other components: Extended pre-purge and blower operation

Sign #4: System Lockouts and Error Codes

What to Look For

The furnace attempts to start but enters a lockout condition, often displaying error codes related to ignition failure:

• LED blinks indicating "Ignition failure"
• LCD displays showing ignition error codes
• Multiple retry attempts before lockout
• System requires manual reset to attempt restart

Understanding Control Board Logic

Modern HVAC control boards monitor the ignition sequence closely:

Timing Windows: The board allows specific time windows for each step:

• Ignitor warm-up: 15-60 seconds (model dependent)
• Proving period: 3-7 seconds
• Ignition confirmation: 3-10 seconds after gas valve opens

If the flame sensor doesn't detect flame within these windows, the system locks out to prevent gas accumulation.

Ignitor-Related Lockout Scenarios

Scenario 1: Ignitor Never Reaches Temperature

• Element has high resistance or open circuit
• Control board times out during warm-up phase
• Diagnostic: Ignitor doesn't glow at all or glows very dimly

Scenario 2: Ignitor Heats But Flame Doesn't Establish

• Ignitor not hot enough for reliable ignition
• Gas flows but ignition is delayed or fails
• Flame sensor times out waiting for flame signal

Scenario 3: Intermittent Operation

• Sometimes ignites successfully, sometimes fails
• Indicates marginal ignitor performance
• Failure rate increases over time

Troubleshooting Beyond the Ignitor

While ignitor failure is common, also verify:

• Gas supply pressure is adequate
• Gas valve is functioning correctly
• Flame sensor is clean and positioned properly
• Burner ports are clean and unobstructed
• Control board is providing correct voltage

Sign #5: Age and Service History

Understanding Ignitor Lifespan

Even without obvious symptoms, ignitor age is a valid replacement criterion. Expected lifespan varies by material and application:

Silicon Carbide Ignitors:

• Residential continuous duty: 2-4 years
• Residential intermittent duty: 3-5 years
• Commercial applications: 1-3 years

Silicon Nitride Ignitors:

• Residential continuous duty: 5-8 years
• Residential intermittent duty: 8-12 years
• Commercial applications: 3-6 years

Factors That Accelerate Wear

Cycling Frequency: Each ignition cycle causes thermal expansion and contraction. Systems that cycle frequently (poorly sized equipment, mild climates) experience more wear.

Continuous vs. Intermittent Duty: Ignitors that remain powered during burner operation (continuous duty) experience constant thermal stress, reducing lifespan by 30-50%.

Environmental Conditions:

• High humidity accelerates degradation
• Dusty environments promote contamination
• Corrosive atmospheres attack terminal connections
• Extreme cold increases thermal shock severity

Proactive Replacement Strategy

For critical applications where downtime is costly, consider:

Preventive Replacement Schedule:

• Silicon carbide: Replace every 3-4 years regardless of symptoms
• Silicon nitride: Replace every 6-8 years in critical applications
• Keep spares on hand for emergency replacement

Tracking and Documentation:

• Record installation date on equipment label
• Log performance metrics during maintenance visits
• Note any abnormal behaviors or symptoms
• Track total number of ignition cycles (if equipment provides this data)

Choosing the Right Replacement Ignitor

Match Original Specifications

When selecting a replacement, verify:

• Voltage rating: 120V or 240V
• Resistance range: Must match control board expectations
• Physical dimensions: Length, width, mounting hole spacing
• Terminal type: Spade, screw, or wire leads
• Mounting configuration: Angle, offset, orientation

Consider Upgrading to Silicon Nitride

If replacing a silicon carbide ignitor, upgrading to silicon nitride offers:

• 2-3x longer service life
• Better reliability in demanding applications
• Improved resistance to thermal shock and contamination
• Faster warm-up times

Verify compatibility with your control board, as silicon nitride's lower resistance and higher current draw may require board adjustments.

Conclusion: Don't Wait for Complete Failure

Hot surface ignitor failure is rarely sudden and catastrophic. In most cases, warning signs appear weeks or months before complete failure. By monitoring for these five indicators, HVAC professionals and facility managers can:

• Schedule replacements during routine maintenance
• Avoid emergency service calls and premium pricing
• Prevent system downtime during peak heating season
• Maintain optimal system efficiency and safety

Remember: A failing ignitor doesn't just risk comfort—it can create safety hazards through incomplete combustion or gas buildup. When in doubt, replace it.