Coleman Furnace Not Igniting: Troubleshooting and Common Fixes

The following guide helps diagnose and repair a Coleman furnace not igniting, covering safety checks, common causes, step-by-step troubleshooting, and when to call a professional. It focuses on practical fixes for pilots, igniters, gas supply, sensors, and control errors.

Symptom	Likely Cause	Quick Action
No pilot or flame	Gas supply, pilot assembly, or valve	Check supply, relight pilot per manual
Clicking but no ignition	Faulty igniter or gas valve	Inspect igniter, listen for gas flow
Ignites then shuts off	Flame sensor, pressure switch, vent blockage	Clean sensor, check venting
No power/reset	Thermostat, fuse, control board	Verify power, replace blown fuse

How Furnaces Ignite: Basic Principles

Understanding ignition helps isolate problems. Modern Coleman furnaces use one of two systems: a standing pilot or an electronic ignition (hot surface igniter or intermittent pilot). The thermostat calls for heat, the control board opens a gas valve, the igniter lights the burner or pilot, and a flame sensor confirms combustion. If any link fails, the furnace will not ignite.

Safety First

Working on a heating appliance requires caution. Turn off power at the service switch and the breaker before inspecting internal components. If a gas odor is present, evacuate the area and call the gas utility or emergency services. If unsure about any step, contact a licensed HVAC technician.

Initial Quick Checks

Before disassembling anything, perform these fast checks that resolve many ignition problems.

• Thermostat Settings: Verify the thermostat is set to heat and the temperature is above room temperature.
• Power Supply: Confirm the furnace switch is on and the breaker isn’t tripped.
• Gas Supply: Ensure the gas valve to the furnace is open and other gas appliances work.
• Air Filter: Replace dirty filters; severely restricted airflow can trip safety limits.

Standing Pilot Furnaces: Pilot Troubleshooting

Older Coleman units with a standing pilot rely on a continuously burning pilot light. If the pilot won’t stay lit, the burner cannot ignite.

Relighting The Pilot

Follow the manufacturer instructions printed on the furnace or in the manual. Typical steps: set thermostat to off, turn gas control to “pilot,” depress the pilot knob and press the igniter or use a long match. Hold for 30–60 seconds before releasing.

Pilot Assembly Problems

Common issues include a clogged pilot orifice, weak thermocouple, or misaligned pilot flame. A weak pilot can blow out or fail to heat the thermocouple sufficiently, causing the gas valve to close.

• Clean The Orifice: Use compressed air or a thin wire to remove soot and debris.
• Check Flame Shape: Pilot flame should envelop the thermocouple; if yellow or shaky, clean burners and check combustion air.
• Replace Thermocouple: If the pilot lights but the furnace won’t stay on, a faulty thermocouple or thermopile likely needs replacement.

Electronic Ignition Systems: Hot Surface And Spark Igniters

Most modern Coleman furnaces use electronic ignition. Problems are typically with the hot surface igniter (HSI), spark module, or flame sensor.

Hot Surface Igniter (HSI)

HSIs glow red to ignite gas. They are fragile and develop cracks or fail after many cycles. Signs of failure include clicking without ignition or no glow at all.

• Visual Inspection: Look for cracks or breaks; replace if damaged.
• Resistance Test: Use an ohmmeter; typical resistance varies by model—consult the furnace manual.
• Replacement: HSIs are replaced as a unit and require careful handling to avoid oils from skin causing premature failure.

Spark Igniters

Spark igniters produce a spark to light the burners. If sparks are absent or weak, inspect for loose wiring, carbon buildup, or a failing control module.

Gas Valve And Pressure Issues

If the igniter works but burners don’t light or light weakly, investigate the gas valve and pressure.

• Gas Valve Operation: Listen for a soft click when the thermostat calls. No click can indicate a failed valve or control board problem.
• Gas Pressure: Low inlet pressure from the service line or regulator issues reduce flow. A qualified technician with manometer tools should test pressure.
• Obstructions: Check gas piping and burners for blockages or spiders/insects in burner ports.

Flame Sensor And Flame Loss

When a furnace lights and then shuts off quickly, the flame sensor may be failing to detect the flame, causing the control board to close the gas valve as a safety function.

• Cleaning: Remove the flame sensor and gently clean the metal rod with fine emery cloth or steel wool to remove oxidation.
• Alignment: Ensure the sensor probe sits in the flame and connections are secure.
• Replacement: If cleaning doesn’t help, replace the sensor; parts are inexpensive and typically straightforward to install.

Pressure Switch, Venting, And Condensate Issues

High-efficiency Coleman furnaces use induced draft blowers and pressure switches to confirm venting. Blocked vents or a stuck pressure switch prevent ignition.

• Check Venting: Inspect intake and exhaust for obstructions, nests, or ice.
• Pressure Switch Tubing: Verify tubing is connected and not cracked or clogged.
• Condensate Trap: Condensing furnaces drain condensate; a clogged trap or float switch can disable the system.

Error Codes And Diagnostic Lights

Many Coleman control boards flash LEDs or display error codes to identify faults. Consult the furnace label or manual for code meanings.

• Record Flash Pattern: Count long and short flashes; this maps to a specific fault like pressure switch open, ignition failure, or limit switch tripped.
• Reset Procedure: Power-cycle the furnace for 30 seconds; repeated resets without resolving the root cause are not recommended.

Control Board, Limit Switches, And Safety Devices

When basic ignition parts check out, control and safety components may be at fault. Limit switches, rollout switches, and the control board itself can interrupt ignition sequences.

• Limit Switches: Overheat or blocked airflow can trip limit switches; ensure airflow and blower operation are correct.
• Rollout Switches: These open if burners are unstable; replacement is required if tripped and cause corrected.
• Control Board: Inspect for burned components or loose connectors. Boards are replaced if diagnostics point to electronic failure.

Tools And Parts Commonly Needed

Item	Purpose
Multimeter	Test continuity, voltage, and resistance
Screwdrivers And Nut Drivers	Access panels and remove components
Replacement Igniter/Flame Sensor	Common wear parts
Compressed Air/Brush	Clean burners and pilot orifices

When To Call A Professional

Call a licensed HVAC technician if any of the following apply: suspected gas leak, gas valve replacement, failed pressure testing, control board diagnostics, or if the homeowner is uncomfortable working with gas or live electrical components. Technicians hold certifications and carry specialized tools for safe, code-compliant repairs.

Estimated Repair Costs And Timeframes

Cost depends on parts and labor. Typical ranges: flame sensor replacement $100–$200, igniter $150–$350, thermocouple $75–$200, control board $300–$800, and gas valve $200–$600. Labor varies by region; emergency calls increase cost. Most common repairs complete within 1–3 hours.

Preventive Maintenance To Avoid Ignition Problems

Routine maintenance prolongs lifespan and prevents ignition issues. Recommended annual tune-ups include cleaning burners, inspecting and replacing filters, checking heat exchanger condition, testing safety controls, and verifying thermostat calibration.

• Change Filters Quarterly: Maintains airflow and prevents limit trips.
• Annual Professional Tune-Up: Ensures safe combustion and efficient operation.
• Keep Vents Clear: Exterior intake/exhaust should be unobstructed year-round.

DIY Troubleshooting Checklist

1. Verify thermostat and power to the furnace.
2. Confirm gas is on and other gas appliances work.
3. Inspect and replace a dirty air filter.
4. If standing pilot, relight and observe pilot flame on thermocouple.
5. For electronic ignition, observe HSI glow or spark; check for cracked HSI.
6. Clean flame sensor and burner ports if furnace lights then shuts off.
7. Check venting, pressure switch tubing, and condensate drain for blockages.
8. Note any LED error codes and consult manual for code meanings.

Helpful Resources And Documentation

Owner manuals and tech sheets contain model-specific procedures and error code charts. Coleman brand documentation is often included on the furnace access panel or available from the manufacturer’s website. For safety or code questions, consult local building departments and licensed contractors.

For parts and wiring diagrams, reference the model number on the furnace rating plate. OEM parts match control boards, igniters, and sensors precisely and reduce diagnostic complexity.

Final Advice

Troubleshooting a Coleman furnace not igniting can often be resolved by following systematic checks: confirm power and gas, inspect ignition components, clean flame sensors and burners, and verify venting and pressure switches. If uncertainty remains or the repair involves gas valves, pressure testing, or extensive disassembly, a licensed HVAC technician should perform the work to ensure safety and compliance with codes.