Furnace igniter not heating — igniter

Use only checks that match the exact appliance or system and its official guide.

1. Check 1

   Set the thermostat to its normal heat mode and raise the set temperature only enough to create an ordinary call for heat. From a safe position, note whether the furnace responds, whether the blower runs, and whether the thermostat or furnace display shows a warning.

   Expected result: The furnace may remain silent, run the blower without heat, start a sequence and stop, or show a manufacturer-specific status light or message.

   Next step: Record the exact response and compare it with the owner's manual. If the thermostat is calling for heat but the sequence repeatedly stops, continue only with the safe observations below and arrange HVAC service.

   Stop if: Do not remove the furnace panel, hold a door switch closed, or use a jumper to force a heat call.

   Why this matters

   Why: A missing heat call, control setting, or system power issue can prevent the igniter stage from being reached. A blower-only response does not prove the igniter is defective.

2. Check 2

   Look at the furnace's accessible power indication and the nearby service switch or breaker without touching wet equipment or opening the cabinet. If the breaker is tripped, leave it off and arrange service; do not reset it repeatedly to make the igniter heat.

   Expected result: The furnace may have no display or response, the service switch may be off, the breaker may be tripped, or the controls may appear powered while ignition still does not start.

   Next step: Photograph or record the indicator state and tell the technician whether the breaker or switch changed. Do not work inside the electrical panel or furnace cabinet.

   Stop if: Stop for a burning odor, smoke, sparks, damaged wiring, wet equipment, heat at the switch, or a breaker that trips again.

   Why this matters

   Why: The igniter and control board need electrical power, but loss of power does not identify whether the cause is the switch, breaker, wiring, control, or another fault. A tripped breaker is a reason to investigate, not an invitation to keep resetting it.

3. Check 3

   Inspect only the normally accessible furnace filter, return opening, and supply registers. If the filter is visibly loaded and the owner's manual identifies a customer-replaceable filter, replace it with the specified type without opening the burner compartment; otherwise leave it in place and record its condition.

   Expected result: The filter may be clean, heavily loaded, missing, incorrectly seated, or impossible to identify safely. Registers may be open, blocked by objects, or unaffected.

   Next step: After one clearly authorized filter change, make one normal heat call and observe whether the startup pattern changes. If the igniter still does not heat or the furnace locks out, stop testing and call an HVAC technician.

   Stop if: Do not remove the blower or burner panel, clean internal burners, or substitute a filter based only on size or appearance.

   Why this matters

   Why: Restricted airflow can contribute to furnace shutdown or poor heating, but a clean filter does not clear the igniter, flame sensor, gas, control, or venting system.

4. Check 4

   During one ordinary heat call, observe the startup sequence only through a manufacturer-provided sight window or external indicator. Do not remove a cover or reach into the furnace. Record whether a hot-surface element glows, a spark is heard or seen through the intended window, a pilot appears when the manual says one should, and whether the main burner lights.

   Expected result: The sequence may stop before ignition, show no glow, click without a flame, light briefly and go out, or complete ignition and still deliver cool air.

   Next step: Stop after one observed sequence and provide the exact pattern to the technician. Do not repeat cycles to force ignition or attempt to clean or reposition the igniter or flame sensor.

   Stop if: Stop immediately for gas odor, delayed ignition, a bang, flame outside the burner area, smoke, unusual flame color, or any warning that requires opening the cabinet.

   Why this matters

   Why: No glow or spark can fit an igniter, power, control, or safety-chain issue; glow or spark without burner ignition can involve gas delivery or burner conditions; a brief flame can involve flame sensing or another safety response. The observation narrows the diagnosis but does not identify a replaceable part.

5. Check 5

   From outside and ground level, look for an obvious obstruction at the furnace intake or exhaust termination, such as snow, leaves, or debris, only if the manufacturer's installation guidance identifies those terminations and the area is safe to approach. Record any blockage without reaching into the pipe or changing the venting.

   Expected result: The termination may be clear, visibly obstructed, damaged, disconnected, or inaccessible from a safe position.

   Next step: Keep the furnace off and call an HVAC professional for any blockage, damage, or uncertainty. Do not disassemble the vent, bypass a pressure switch, or use the furnace until a qualified person confirms safe operation.

   Stop if: Leave immediately for a carbon-monoxide alarm, gas odor, headache, dizziness, nausea, unusual combustion noise, or a vent that is disconnected or damaged.

   Why this matters

   Why: Blocked or damaged venting can stop a furnace through a safety control and can create a combustion or carbon-monoxide concern. A clear termination does not rule out an internal vent, pressure, heat-exchanger, or control problem.