Furnace ignitor not glowing: trace the heat sequence

If your furnace ignitor is not glowing, do not assume the ignitor is bad. The control may have stopped at an earlier safety step, and some furnaces use spark or pilot ignition rather than a glowing hot-surface ignitor.

The useful question is: What was the last confirmed step before ignition stopped? Keep the furnace assembled, record one normal heat-call sequence and the exact board code, and use the current manual for the complete model. Do not jumper a safety, force ignition, handle the gas valve, or probe energized equipment.

First confirm whether the furnace should glow

Many modern gas furnaces use a silicon carbide or silicon nitride hot-surface ignitor (HSI) that becomes visibly bright before the gas valve opens. Other equipment may use direct spark, intermittent pilot, or another ignition design. Those systems can ignite normally without an HSI-style glow.

Check the owner’s literature, service record, or manufacturer documentation for the exact model. Carrier’s furnace ignitor overview likewise distinguishes hot-surface, spark, and pilot ignition and directs electrical and gas-component work to trained professionals.

If you cannot see the ignition area through a factory viewing port, do not remove or defeat a door to watch it. Opening a panel can operate an interlock, expose live or combustion components, and change the sequence you are trying to observe.

Furnace ignitor not glowing: sequence map

A common hot-surface-ignition furnace moves through the stages below. Exact order, delays, and safety logic vary, so treat this as a classification map rather than a universal test procedure.

Sequence stage	Safe observation	What the stop may direct a technician to check	What it does not prove
Thermostat call	The thermostat shows a heat call, or the call disappears before equipment starts	Thermostat settings, schedule, power, wiring, zoning, or control input	That the ignitor is faulty
Inducer start	A small combustion-air blower starts before ignition; do not confuse it with the larger circulating blower	Control output, inducer, wiring, a safety circuit, or model-specific start logic	That every motor sound is the inducer
Pressure proof	The inducer runs, but the expected ignition step never follows	Intake, exhaust, condensate, sensing path, pressure-switch circuit, draft, or control logic	That the pressure switch itself failed
Board command and glow	Earlier steps appear complete, but no HSI glow is visible and a code may appear	Ignitor, connector, wiring, ignition-control output, supply conditions, or control	Which component failed without model-specific tests
Gas and burner ignition	The HSI glows, but stable burner flame does not appear	Fuel availability, gas-valve command, ignitor position or performance, burners, or control	That the flame sensor caused a pre-flame failure
Flame proof	Burners light, then shut off shortly afterward	Flame stability, carryover, sensing, grounding, polarity, wiring, gas, venting, or control	That the ignitor is responsible for the shutdown

Current Goodman/Amana/Daikin service literature for the covered furnace families places inducer operation and pressure-switch proof before the ignitor is energized. Current Lennox installation instructions for the covered model show the same broad order: thermostat call, inducer, pressure proof, pre-purge, ignitor warm-up, gas, then flame proof. Neither sequence should be generalized into universal timing, code, voltage, or resistance values.

What each no-glow pattern means

Nothing starts after the thermostat calls

Confirm the thermostat is in heat mode, the setpoint is above room temperature, and an owner-accessible disconnect or breaker has not been switched off. Record any blank display or loss of the heat indicator.

Do not open the furnace or keep cycling power. A power, thermostat, interlock, control, or safety condition can prevent the sequence from reaching the inducer, well before an ignitor decision is possible.

Use the furnace inducer motor no-start guide to separate silence, humming, starts-and-stops behavior, and a running inducer that never proves draft. Those patterns belong before the ignitor branch and do not justify an ignitor replacement.

The inducer runs, but the ignitor never glows

This pattern often means the sequence has stopped between inducer start and ignition. A draft-proving requirement, vent or intake condition, condensate problem, sensing path, safety circuit, wiring, or control response may be involved.

It does not automatically mean “replace the pressure switch.” Use the furnace pressure-switch code guide to understand this earlier branch without bypassing the switch or disturbing its tubing.

The board shows an ignitor or ignition code

Photograph the code before power is interrupted, then find the legend on the furnace or in the exact model manual. Flash counts and code numbers are not universal. A code can describe an open circuit, failed sequence, retry, lockout, relay condition, or another model-specific state without naming the root cause.

Copeland’s White-Rodgers control instructions, for example, define codes for one covered replacement control. That legend applies to that control—not every furnace displaying the same number of flashes.

The ignitor glows, but there is no flame

No-glow troubleshooting ends once the HSI visibly operates. The next branch includes gas availability, gas-valve command, ignitor position or heat output, burner ignition, and control logic. Do not touch gas controls, attempt a manual light, or force the gas valve or ignition sequence.

Flame appears and then goes out

The furnace has moved beyond the no-glow branch. Follow the furnace flame-sensor symptom guide to separate lost flame proof from a guessed sensor failure. If the system repeats the sequence or ends the heat call at a later stage, the broader furnace short-cycling diagnostic will help classify the timing.

Safe checks before calling for service

Homeowners can collect useful evidence without entering the service compartment:

1. Check for an emergency. If a CO alarm sounds, anyone has possible carbon-monoxide symptoms, or you see smoke, soot, or flame outside its normal enclosed location, move everyone outside and call 911. If you smell gas or hear hissing, leave without operating switches and contact emergency services or the gas utility from outside. Follow the carbon-monoxide and HVAC safety guide before reentry.
2. Confirm the equipment and ignition type. Record the brand and complete model from paperwork or a safely accessible label. Do not assume every gas furnace has a visible HSI.
3. Record one heat call. Note the thermostat call, motor sounds, visible glow, burner flame, circulating-blower operation, retries, and shutdown in order. Observe through a factory port only.
4. Preserve the fault. Photograph the display or status light and note whether it is active or stored. Repeated resets can erase evidence and do not correct the cause.
5. Look only at safe exterior conditions. From ground level, note snow, ice, leaves, or damage at a visible intake or exhaust termination. Do not climb, insert tools, or dismantle venting.
6. Prepare the handoff. Put the model, code, timing, weather, recent work, and safety observations in the HVAC maintenance log.

A filter check is sensible routine maintenance when the manual allows owner access, but a clean filter does not prove an ignitor circuit is healthy or explain a sequence that stopped before ignition.

How a qualified technician should narrow the cause

A defensible service report should identify the exact model literature, reproduce the heat call, retrieve active and stored faults, and state the last completed sequence step. The technician can then inspect the applicable safety, draft, venting, condensate, connection, ignitor, wiring, control, and supply branches under the manufacturer’s procedures.

Electrical values, test points, acceptable readings, and ignitor types are model-specific. The technician—not the homeowner—should decide which de-energized inspections and controlled operating tests are required, use suitable instruments, and document the evidence before replacing a part. Universal online resistance or voltage numbers are not a substitute for the manual.

After correction, the service record should show a complete verified heat cycle, proper ignition and flame carryover, safety-control operation, and any required gas, combustion, venting, temperature-rise, or airflow checks. Our DIY vs. professional HVAC repair guide explains why cabinet-open electrical and combustion work belongs with qualified service personnel.

Sources and further reading

• Goodman/Amana/Daikin: service and troubleshooting manual for covered gas furnaces
• Lennox: installation instructions and heating sequence for the covered furnace
• Carrier: furnace ignitor types, symptoms, and service boundary
• Copeland/White-Rodgers: integrated hot-surface ignition control instructions
• U.S. CPSC: 2026 furnace and carbon-monoxide safety guidance

Your next step

Send a qualified HVAC company the complete model, exact fault code, and the ordered observations from one heat call. Ask the technician to identify the last completed sequence step and show the model-specific evidence before authorizing an ignitor, pressure switch, control, or gas-related repair.

No glow is a symptom location, not a parts diagnosis. Following the sequence protects the furnace’s safety logic and makes the service call faster and more defensible.