The article explains common causes and practical troubleshooting steps when an American Standard furnace is not igniting, offering safe diagnostics, likely repairs, estimated costs, and maintenance tips to restore reliable heating. This guide is written for a general U.S. audience and emphasizes clear, actionable information without specialized certification assumptions.
| Symptom | Possible Cause | Quick Action |
|---|---|---|
| No flame or ignition | Ignitor, pilot, gas valve | Check power, thermostat, gas supply |
| Clicking but no light | Ignitor failure, weak gas pressure | Inspect ignitor and pressure switch |
| Short ignition sequence | Flame sensor dirty | Clean flame sensor |
| System locks out | Safety limit or pressure switch | Reset and investigate blocked vents |
How Furnaces Ignite: Basic Components To Know
An American Standard gas furnace typically uses an electronic hot surface ignitor or a standing pilot to light the burners, with inputs from a thermostat, gas valve, flame sensor, pressure switch, and control board.
Hot Surface Ignitor heats red-hot to ignite gas. Flame Sensor verifies flame presence. Gas Valve controls fuel delivery. Pressure Switch ensures proper venting. Understanding these parts helps pinpoint why the furnace is not igniting.
Safety First: Precautions Before Troubleshooting
Working with gas and electrical components requires care. Always turn off power at the furnace switch or breaker and shut the gas off if a leak is suspected. If the smell of gas is present, evacuate the home and contact the gas company or emergency services immediately.
Use a non-contact voltage tester before touching components. If uncomfortable with electrical or gas work, hire a licensed HVAC technician. Safety overrides troubleshooting speed.
Initial Diagnostics: Quick Checklist
These checks take only a few minutes and often reveal the issue. Confirm the thermostat is set to heat and temperature is above the room temperature. Ensure the furnace switch and breaker are on.
Verify the gas supply: check the gas shutoff valve at the furnace and, if applicable, a main gas meter valve. Inspect air filters and vents; extremely dirty filters can cause lockouts. Look for error codes or LED blink patterns on the furnace control board and consult the owner’s manual.
Common Causes And How To Fix Them
1. Thermostat Or Controls
If the thermostat fails to call for heat, the furnace won’t ignite. Replace batteries in battery-powered models and ensure thermostat wiring connections are secure.
To test, set the thermostat several degrees higher or jump the R and W terminals at the furnace to simulate a call for heat. If the furnace starts, replace or recalibrate the thermostat.
2. Power Supply And Fuses
Furnaces need 120V for controls. A tripped breaker, blown fuse, or switched-off service switch will prevent ignition. Check the home electrical panel and the furnace’s dedicated breaker.
Some systems include an internal fuse on the control board. Replace a blown fuse with the exact type and rating. Persistent fuse failures indicate a deeper electrical fault requiring a technician.
3. Gas Supply And Valve Problems
Confirm the gas valve to the furnace is open and the home’s gas service is functioning. If gas is on but burners don’t light, the internal gas valve or solenoid may be faulty.
Repairing or replacing a gas valve should be done by a licensed technician due to gas-tightness and safety regulations. Expect part and labor costs to vary widely by region.
4. Ignitor Failure (Hot Surface or Spark)
Hot surface ignitors (silicon carbide or nitride) become brittle and fail over time. Signs include the furnace trying to ignite but shutting off without lighting or seeing the ignitor glow then crack.
Visual inspection often reveals cracks. Testing with a multimeter can confirm open circuit. Replacement is a common DIY task if comfortable handling components; otherwise call a pro. Keep a compatible OEM part number for ordering.
5. Dirty Or Faulty Flame Sensor
A flame sensor that is dirty or corroded can fail to detect flame, causing ignition to shut off quickly. This results in repeated ignition attempts followed by lockout.
Cleaning the flame sensor with fine emery cloth or steel wool and reinstallation often restores function. Avoid aggressive scraping; replace if sensor is pitted or damaged.
6. Pressure Switch And Inducer Motor Issues
The inducer motor creates the draft for safe venting; the pressure switch confirms the inducer is functioning. If the inducer fails or the pressure switch tubing is blocked or cracked, the furnace will not proceed to ignition.
Listen for the inducer running. Inspect tubing for condensation or blockages and replace faulty pressure switches. Inducer motor replacement generally requires professional service.
7. Condensation And Vent Blockages
High-efficiency furnaces produce condensate. Clogged drain lines or blocked PVC vents can trigger pressure switch trips and prevent ignition.
Inspect outdoor vents for debris, birds’ nests, or snow. Clear condensate drains and check the trap. Regular maintenance prevents recurring failures.
8. Limit Switch And Safety Controls
Limit switches prevent overheating. If blocked airflow or a failed blower causes high temperatures, the limit switch may stay open, inhibiting ignition.
Replace clogged filters, ensure return vents are open, and test or replace malfunctioning limit switches. Persistent trips signal an airflow or blower motor issue requiring deeper diagnostics.
Step-By-Step Troubleshooting Flow
- Confirm thermostat call for heat and power to furnace.
- Check circuit breaker, furnace switch, and control board LEDs for codes.
- Inspect and replace dirty filter; verify airflow and vents.
- Observe ignition sequence: is the inducer running? Does the ignitor glow/click?
- If ignitor glows but no ignition, check gas supply and flame sensor.
- If clicking but no glow, replace ignitor or check spark module.
- Investigate pressure switch and venting if inducer won’t start or trips.
- If locked out, follow manual reset procedure and monitor for recurrence.
When To Clean Parts Versus Replace Them
Cleaning can resolve flame sensor and minor venting issues. Replace components that are cracked, pitted, or fail electrical tests.
Replace ignitors when cracked or open-circuit. Replace flame sensors if cleaning does not restore reliable flame detection. Replace pressure switches or inducer motors when mechanical failure or repeated trips occur.
Estimated Costs And Timeframes
Costs vary by region and furnace model. A replacement ignitor typically ranges $50–$150 for parts and $150–$400 with labor. Flame sensor parts are often $20–$80; labor increases total to $100–$250.
Inducer motors and gas valves are more expensive: expect $300–$800 parts plus labor. Minor cleanings and diagnostics may be inexpensive or included in a maintenance visit.
Maintenance Tips To Prevent Future Ignition Problems
Regular maintenance reduces failures. Replace disposable filters every 1–3 months depending on load and pets. Schedule annual HVAC tune-ups, including ignitor, flame sensor cleaning, vent inspection, and gas safety checks.
Keep outdoor vents clear, maintain proper clearance around the furnace, and install carbon monoxide detectors near sleeping areas to ensure safety after repairs or maintenance.
When To Call A Professional
Call a licensed HVAC technician for these situations: suspected gas leak, cracked heat exchanger, repeated lockouts after basic fixes, electrical shorts, or when component replacement requires gas-valve work.
Professionals provide precise diagnostics, access to OEM parts, and safety compliance. For warranty-covered systems, use authorized service providers to preserve warranty terms.
Parts, Manuals, And Resources
Locate the furnace model number on the interior door panel and reference the American Standard manual for diagnostic LED codes and part numbers. OEM replacement parts ensure fit and performance.
Manufacturer resources, local HVAC supply houses, and reputable online parts retailers can assist with parts and compatibility. Keep the user manual and wiring diagrams for future troubleshooting.
Frequently Asked Questions
Why Does The Furnace Click But Not Ignite?
Clicking without ignition often indicates a failed ignitor or insufficient gas pressure. It may also be a control board or spark module issue in older models. Inspect the ignitor and gas supply first.
What Does A Lockout Mean?
Lockout occurs after multiple failed ignition attempts to prevent unsafe gas flow. Resetting temporarily may restore function, but underlying causes must be addressed to prevent recurrence.
How Long Does An Ignitor Last?
Hot surface ignitors typically last 3–10 years, depending on cycles and system stress. Inspect annually and replace at first sign of cracking or irregular operation.
Key Takeaways
Systematic diagnostics—starting with power, thermostat, and filters—often resolves ignition issues quickly. Components most commonly at fault are the ignitor, flame sensor, pressure switch, and gas valve.
Safety is paramount: stop and call professionals when gas leaks, electrical faults, or complex gas-valve work are suspected. Regular maintenance prevents many ignition failures and extends furnace life.