Keystone Furnace Not Lighting: Troubleshooting and Fixes

The Keystone furnace not lighting can leave a home cold and homeowners frustrated. This article explains why a Keystone gas furnace may fail to ignite, step-by-step troubleshooting to attempt safely, common repairs and estimated costs, and when to call a licensed HVAC technician. It focuses on practical, actionable guidance for U.S. homeowners while highlighting safety precautions.

Symptom	Likely Cause	Quick Fix
No pilot or ignition	Pilot outage / faulty ignitor	Relight pilot or check spark/electronic igniter
Clicking but no flame	No gas to burners / faulty gas valve	Check gas supply; call technician
Short run then shuts off	Dirty flame sensor / clogged burners	Clean flame sensor and burners

How Keystone Furnaces Ignite

Understanding ignition helps isolate problems. Modern Keystone gas furnaces typically use either a standing pilot or an electronic ignition system (hot surface ignitor or spark ignitor). The thermostat calls for heat, the control board opens the gas valve, and the ignitor creates a flame or lights the pilot. A flame sensor confirms combustion and keeps the gas flowing.

Primary Causes Why A Keystone Furnace Is Not Lighting

Pilot Light Or Ignitor Failure

For furnaces with a standing pilot, the pilot may be out due to drafts or a faulty thermocouple. For electronic systems, a failed hot surface ignitor or spark electrode prevents ignition. Ignitors are fragile and can fail with age or power surges.

Gas Supply Issues

No gas to the furnace stops ignition. Causes include a closed gas shutoff, turned-off meter, interrupted utility supply, or a failing gas valve. Smell of gas requires immediate evacuation and calling the gas company.

Thermostat Or Wiring Problems

If the thermostat fails to signal a call for heat or wiring is damaged, the furnace won’t initiate ignition. Faulty thermostat settings or a dead thermostat battery can mimic ignition failure.

Flame Sensor Malfunction

A dirty or failing flame sensor won’t detect combustion and the control board will shut off the gas after a few seconds. This common issue often causes the furnace to light briefly then shut down.

Clogged Burners And Airflow Restriction

Accumulated dirt, rust, or insect nests in burners can prevent consistent combustion. Restricted airflow due to dirty filters or blocked vents can also cause flame instability and ignition failure.

Control Board, Limit Switch, Or Safety Interlock Failures

The furnace control board, limit switch, or pressure switch could fail or sense unsafe conditions and disable ignition. Diagnostic lights on the furnace control board often indicate these faults.

Safety First: Precautions Before Troubleshooting

Always prioritize safety. Turn off power and gas before inspecting internal parts. If there is a gas odor, leave the house immediately and call the gas company or emergency services. Only perform visual checks and basic resets unless comfortable working with gas appliances.

Step-By-Step Troubleshooting For A Keystone Furnace Not Lighting

1. Check Thermostat And Power

Confirm thermostat is set to heat and temperature setpoint is above room temperature. Replace batteries if applicable. Ensure furnace power switch and circuit breaker are on. Many “not lighting” issues start with thermostat or power problems.

2. Inspect The Furnace For Error Codes

Open the access panel and locate the control board LED. Count blink codes or check the digital display and consult the furnace manual for code interpretation. Error codes narrow down the likely cause quickly.

3. Verify Gas Supply

Ensure the gas valve at the furnace is open and the home’s gas meter or main valve is on. If other gas appliances work but the furnace doesn’t, the issue is likely internal. If the gas feels off or there’s no gas flow, contact the utility.

4. Relight Standing Pilot (If Equipped)

Follow the furnace label instructions to relight the pilot. Hold the pilot gas button as directed and use a long lighter or the built-in igniter. If the pilot won’t stay lit, the thermocouple may be faulty or misaligned.

5. Inspect And Replace Ignitor

For electronic ignition systems, visually inspect the hot surface ignitor for cracks or glowing issues. Do not touch a hot surface ignitor with bare hands. If cracked or not glowing, replacement is usually required and can be done by a technician or a confident DIYer with the right part.

6. Clean The Flame Sensor

Remove and gently clean the flame sensor rod with fine sandpaper or steel wool to remove oxidation. Reinstall and test. Cleaning often resolves short-run or shutdown issues when the furnace lights but then goes out.

7. Check Burners And Flame Pattern

Inspect burners for rust, debris, or misalignment. The flame should be steady blue with minimal yellow tips. Sooty, flickering, or yellow flames indicate incomplete combustion and require cleaning or adjustment.

8. Inspect Air Filter, Blower, And Vents

A clogged filter or blocked return vents can trigger high-limit switches that prevent ignition. Replace dirty filters and ensure vents and returns are unobstructed to allow normal airflow.

9. Test The Gas Valve And Pressure Switch

If the ignitor functions but burners don’t light, the gas valve or pressure switch may be failing. These checks often require a multimeter and gas pressure gauge and are best handled by a licensed technician.

When To Call A Professional

Call a licensed HVAC technician if troubleshooting steps don’t restore ignition, if diagnostic codes point to control board or gas valve failures, or if any work requires gas valve or burner disassembly. Technicians can safely test gas pressure, replace electronic components, and validate combustion safety.

Typical Repair Costs And Timeframes

Costs vary by region and exact fault. Typical ranges: ignitor replacement $100–$300, flame sensor cleaning or replacement $75–$200, control board replacement $300–$800, gas valve replacement $200–$600. Emergency service and extensive diagnostics increase cost and time.

Parts And Tools Commonly Needed

• Replacement hot surface ignitor or spark electrode
• Flame sensor rod
• Multimeter for electrical checks
• Fine sandpaper for cleaning sensors
• Screwdrivers, nut drivers, flashlight
• Manufacturer-specific replacement parts (match furnace model)

Maintenance Tips To Prevent Ignition Failure

Regular maintenance reduces ignition problems. Replace air filters every 1–3 months, schedule annual professional tune-ups, keep the furnace area clean, and ensure vents and returns remain unobstructed. Annual inspection of the ignition system and burners prevents most common failures.

How To Read Control Board Diagnostic Codes

Keystone furnaces often use LED blink patterns or digital readouts. Count blink intervals and consult the furnace manual or the label inside the access panel for a code chart. Common codes include ignition failure, pressure switch fault, and flame loss.

Common FAQs About Keystone Furnaces Not Lighting

Why Does The Furnace Click But Not Ignite?

Clicking indicates the control board is attempting ignition but the ignitor or gas supply is missing. Possible causes: failed ignitor, blocked gas valve, or wiring issues.

Why Does The Furnace Light For A Few Seconds Then Shut Off?

This is often a dirty flame sensor or a flame rollout/limit switch problem. The furnace senses no flame or unsafe conditions and shuts off the gas as a safety measure.

Can A Homeowner Replace The Ignitor?

A competent DIYer can replace a visible ignitor following safety procedures, but handling fragile components and working near gas valves requires caution. When in doubt, hire a professional.

Is A Gas Smell Normal When The Furnace Tries To Ignite?

No. A persistent gas smell is dangerous. Leave the premises and call the gas company or emergency services immediately. Do not operate electrical switches or the furnace.

Resources And Links

For specific part numbers and wiring diagrams, consult the Keystone furnace model label and owner’s manual. Manufacturer tech sheets and HVAC trade sites provide wiring diagrams and diagnostic code charts for accurate troubleshooting.

Professional inspection is recommended if local codes require licensed contractors for gas appliance repairs. Prioritize safety and proper combustion testing after repairs.