Burner Lockout Repair
Furnace Flame Sensor Repair in Sioux Falls, SD
If your furnace lights for three to seven seconds and then shuts down — over and over — the flame sensor is the first suspect. It is a small part with an outsized effect on winter comfort.
For service availability, please have your 5-digit ZIP code ready.
What the Flame Sensor Actually Does
The flame sensor is a thin metal rod in the burner flame path. It does not create heat; it confirms that flame is present by passing a tiny current — measured in microamps — through the flame to ground. If the control board does not see that signal, it closes the gas valve within seconds as a safety response.
Over time, combustion byproducts build a thin oxide film on the rod. That film blocks the signal even though the flame is perfectly normal, so the furnace shuts itself down unnecessarily.
Symptoms of a Dirty or Failing Flame Sensor
- Burner lights and goes out within a few seconds, repeatedly.
- Furnace locks out after three ignition attempts and requires a reset.
- Heat works intermittently, often better after the system has been off a while.
- Vents blow cool air between failed cycles.
- The control board flashes a flame-sense or lockout error code.
Cleaning vs. Replacement
Most of the time a flame sensor can be carefully cleaned and re-tested. We measure the microamp signal before and after cleaning: a healthy reading is well above the board's minimum threshold, and a sensor that only marginally recovers gets replaced rather than left to fail again in a month.
We also confirm the ground path and burner condition. A weak flame signal can be caused by a poor chassis ground or dirty burners rather than the sensor itself, and replacing the rod would not fix either one.
What to Expect From the Service Visit
Real diagnosis first
Plain-language explanation
Price before the work
Homeowner Questions
Frequently Asked Questions
How often do flame sensors need cleaning?+
Many residential furnaces benefit from a flame sensor cleaning during annual maintenance, especially systems that run long heating seasons.
Is a flame sensor repair expensive?+
It is usually one of the less expensive residential furnace repairs, particularly when performed during business hours. Use the cost calculator for a planning range.
Can I clean the flame sensor myself?+
Some homeowners do, using fine abrasive pads with the power and gas off. If you are not confident shutting the system down safely and re-seating the sensor correctly, have it serviced.
Why does my furnace work fine some days?+
A marginal flame signal can be just strong enough on some cycles and not others, especially as burners heat up. That is a classic pattern for a sensor approaching failure.
Will a new flame sensor stop the lockouts?+
It will if the sensor is the cause. If the problem is grounding, burner condition, gas pressure, or the control board, replacing the sensor alone will not solve it — which is why we test rather than assume.
Local Contact
Reach a Residential Furnace Technician
For service availability, please have your 5-digit ZIP code ready.
What to have ready
- Your 5-digit ZIP code so we can confirm service availability.
- Furnace brand and approximate age, if you know them.
- What the system is doing: no heat, cold air, noise, or repeated cycling.
- Whether the thermostat screen is on and what it is set to.
Keep Reading
Related Residential Furnace Pages
Need Furnace Repair in Sioux Falls Today?
Residential-only service, 24/7 emergency availability, and a free quote over the phone. Tell us what your furnace is doing and we will walk you through next steps.
For service availability, please have your 5-digit ZIP code ready.