What, where, why, how, by whom—and when?
| What | Clean an applicable flame-proving component where testing supports that remedy. |
|---|---|
| Why | Restore suitable proving when contamination is the established issue, without overlooking wiring or combustion causes. |
| How | Assess the sequence and relevant signal, use the approved service method and verify proving after reassembly. |
| Where | At the flame-sensing component and its relevant circuit in the installed furnace, not at an unrelated room-air sensor. |
| By whom | A qualified professional handling the ignition and combustion system through the appropriate registered business. |
| When / how often | Inspect as the equipment procedure requires. Clean for a supported condition rather than at a universal monthly or yearly frequency. Recurrent ignition shutdown needs diagnosis when it appears, not repeated owner cleaning or resets. |
What, why, when and who
A flame sensor is part of the control system that proves the presence of flame on applicable furnaces. Cleaning is a professional service decision when inspection and testing support it and the model permits that procedure. It is not a universal cure for a burner that starts and stops. The work involves the ignition and combustion system, so qualified service is appropriate rather than treating it as a consumable change. The technician should distinguish a contaminated sensing surface from a damaged sensor, connection issue, grounding problem or another condition. The page explains what competent service looks like without giving a dismantling or abrasive-cleaning recipe.
Symptoms: a brief flame is only a clue
A homeowner may report that the furnace attempts ignition, produces heat briefly and then stops, sometimes with a lockout indication. That pattern can suggest a flame-proving investigation, but the exact sequence must be established. Record the visible status code and timing from an accessible viewing point without opening the appliance. An igniter operating without established flame is a different observation from flame present but not correctly proved. Avoid repeated resets or attempts to make the furnace run longer. Gas smell, a CO alarm or an alarming ignition event overrides ordinary troubleshooting and requires the appropriate emergency response.
Diagnosis: establish the proving problem
The technician follows the ignition sequence and checks whether flame is established, whether the control receives the expected proving signal and what relevant conditions affect it. Sensor position, condition, wiring, connections and grounding can matter on applicable equipment. A fault indication naming flame does not by itself prove the sensing rod is dirty. Ask whether cleaning is supported by evidence or proposed only as a trial. If another combustion or control issue is found, that needs its own scope. A competent explanation identifies the failed condition rather than replacing several related parts in succession without a clear diagnostic basis.
Equipment: flame signal and other relevant tests
On equipment using flame rectification, a technician may measure the flame signal in microamps using the manufacturer’s specified method and compare it with that model’s requirements. Electrical tests can help assess the circuit and connections. Combustion or fuel-pressure checks may be appropriate where the findings call for them. There is no single flame-current threshold to publish for every furnace. A photo of the rod cannot replace an operating test. Ask which measurements were required and whether a before-and-after result was recorded. These are professional diagnostic tasks; homeowners should not bridge the sensing circuit or adjust burner operation.
Work performed: follow the model’s permitted procedure
Where cleaning is justified, the technician isolates the appliance, accesses the component appropriately and uses a method permitted for that part. Fragile insulation, positioning and connections must be protected. Not every sensing component can be treated with the same abrasive or solvent. A damaged component may require replacement rather than repeated cleaning. The cause of poor proving, including a connection or grounding issue where established, also needs correction. Any disturbed assembly must be restored correctly. The invoice should distinguish cleaning, circuit repair and part replacement instead of describing every outcome as the same flame-sensor service.
Verification: prove operation after the work
The technician checks the relevant ignition sequence and flame-proving performance after reassembly. Where measured, the signal should be interpreted against model requirements under the applicable operating conditions. Repeated normal cycles may be needed when the complaint was intermittent. Ask whether the original shutdown has been reproduced or resolved and whether combustion or other checks were required by the work. A furnace that lights once after the control is reset is not by itself proof of a completed repair. Keep any remaining limitation explicit and follow operating restrictions rather than clearing another lockout to continue heating.
Documentation: retain the cause and proving results
Ask for the symptom, sensor condition, cause established, work performed and applicable test results. Where flame current was measured, retain the values, units and operating condition, not only a notation that the sensor was cleaned. The report should state if a part was replaced or a circuit issue corrected and list any unresolved concern. Keep this record with the model information so a recurrence can be compared accurately. For Toronto service planning, describe equipment access and authority to approve work. Confirm the actual contractor and charges directly; a detailed guide is not a claim that this website personally performed the visit.
Related service decisions
Read the related guide · All 20 furnace services · Find a symptom · Do we offer furnace service in your area?
Sources and application
Technical procedures and acceptable values must come from the installed model’s instructions. This page describes service decisions rather than a universal test procedure. Official technical and safety sources →