Your furnace clicks but won’t fire up — that’s the classic sign of a failed ignitor. Before you call for emergency heat repair, many homeowners can safely diagnose and replace this $20–$40 part in under an hour. But skipping safety checks or misdiagnosing the issue could leave you cold — or worse.
Quick Diagnosis
A failed ignitor isn’t always the culprit. Rule out these common causes first:
- No power to the furnace (check breaker and switch near unit)
- Clogged air filter restricting airflow and triggering safety lockout
- Dirty flame sensor preventing ignition sequence from continuing
- Gas valve closed or supply interrupted (smell gas? Stop and evacuate immediately)
- Control board error codes (consult your furnace manual for blinking light patterns)
Tools & Materials Needed
| Item | Purpose | Estimated Cost |
|---|---|---|
| Non-contact voltage tester | Verifies power is off before touching wiring — critical safety step | $15–$25 |
| Phillips and 1/4" hex screwdrivers | Removes access panels and ignitor mounting hardware | $8–$12 |
| Replacement hot-surface ignitor (model-specific) | Must match OEM part number — generic substitutes often fail prematurely | $22–$38 |
| Work gloves and safety glasses | Protects hands from sharp edges and eyes from dust/debris | $10–$18 |
| Shop vacuum with brush attachment | Cleans dust and debris around ignitor mount and burner assembly | $30–$65 |
Step-by-Step Fix
Follow this sequence only after confirming power is OFF at both breaker and furnace switch:
- Locate and inspect the ignitor: Open the furnace’s lower access panel. The ignitor is a small ceramic rod mounted near the burners — look for cracks, glazing, or white residue.
- Test continuity with a multimeter: Set to ohms (Ω). Touch probes to ignitor leads. A good ignitor reads 40–90 ohms. Infinite resistance = failed.
- Disconnect and remove old ignitor: Unplug wiring harness (note orientation), unscrew mounting bracket, and gently pull ignitor straight out — avoid twisting or bending.
- Install replacement: Insert new ignitor fully into its slot, secure bracket screws snugly (don’t overtighten), reconnect harness matching original orientation.
- Restore power and test: Turn on furnace switch and breaker, then set thermostat to heat. Watch through sight glass: ignitor should glow cherry-red for 15–30 seconds before burners ignite.
When to Call a Pro
Stop and call an HVAC technician if any of these apply:
- You smell gas at any point during inspection or repair
- The ignitor glows but burners never light (points to gas valve, pressure switch, or control board issues)
- Furnace displays error code 14, 33, or E1 (common on Lennox, Carrier, and Trane units indicating combustion failure)
- You’re uncomfortable working inside a gas appliance — especially with high-voltage ignition circuits
- Your furnace is under warranty; DIY repairs may void coverage
Prevention Tips
Extend ignitor life by maintaining clean airflow and minimizing thermal stress:
- Replace furnace filter every 1–3 months (more often with pets or allergies)
- Vacuum burner assembly and ignitor area annually — dust buildup causes overheating
- Ensure return air grilles aren’t blocked by furniture or rugs
- Have a licensed technician perform full system tune-up every fall — they’ll check voltage delivery to the ignitor and clean flame sensor
Can I clean a cracked ignitor instead of replacing it?
No. Cracks compromise structural integrity and electrical resistance. Even hairline fractures cause inconsistent heating and premature failure. According to the Furnace Flame Sensor Cleaning Guide, cleaning helps only the sensor — not the ignitor. Replacement is the only safe option.
How long should a furnace ignitor last?
Most hot-surface ignitors last 3–7 years, depending on runtime and maintenance. The U.S. Department of Energy notes that furnaces operating over 1,200 hours per heating season see 30% shorter ignitor lifespan due to thermal cycling fatigue (DOE Residential HVAC Maintenance Report, 2022).
Why does my ignitor glow but no flame appears?
This points beyond the ignitor — likely a gas valve failure, blocked orifice, faulty pressure switch, or insufficient gas pressure.
"Over 68% of 'glow-but-no-flame' cases involve either a dirty pressure switch diaphragm or a failing gas valve — not the ignitor itself," says HVAC Technician Certification Board lead trainer Marcus Lee (2023).Diagnosing these requires manometer testing and voltage tracing best left to pros.
Is it safe to bypass the ignitor to get heat temporarily?
Never bypass or jumper an ignitor. Doing so risks uncontrolled gas release, delayed ignition, and potential explosion. Modern furnaces have multiple safety interlocks precisely because of this hazard. If you need immediate heat, use space heaters rated for indoor use and ventilated rooms — and schedule service right away.
What’s the difference between spark and hot-surface ignitors?
Hot-surface ignitors (ceramic rods) glow red-hot to ignite gas — used in 90%+ of modern furnaces. Spark ignitors (like pilot lights) create intermittent arcs — found mostly in older or commercial units. Replacing one type with the other is incompatible and dangerous. Always match your furnace’s OEM specification — check the furnace manual download page for your model’s exact part number.
Can a dirty filter cause ignitor failure?
Indirectly, yes. A clogged filter reduces airflow, causing the heat exchanger to overheat and trigger high-limit shutdowns. Repeated cycling stresses the ignitor thermally, accelerating wear. The American Gas Association estimates that 22% of premature ignitor failures stem from chronic airflow restriction (AGA Technical Bulletin #HVAC-2021-07).
A working ignitor is essential — but it’s just one link in a chain of precision components. When you fix it right, you restore reliable heat and avoid cascading failures. If your furnace still hesitates after replacement, revisit the flame sensor or consult a certified technician — because sometimes the real problem hides just behind the part you replaced.