mypros+
Error code reference

Goodman Hvac Error Code 5

False flame sensed by the ignition control, indicating a sticking gas valve or flame sense circuit issue.

Goodman codesGoodman hvac codes

False flame sensed by the ignition control, indicating a sticking gas valve or flame sense circuit issue.

First step from the service manual

Check for sticking gas valve; replace if confirmed.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for 5.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What 5 means on a Goodman hvac

Goodman error code 5 indicates that the ignition control module is detecting a flame signal when no flame should be present. This is referred to as a "false flame" condition. The ignition control continuously monitors the flame sense circuit during operation and, critically, also checks for flame signal presence during the pre-purge and post-purge periods when the gas valve should be closed. If a flame signal is detected outside of a normal ignition sequence, the control board logs fault code 5 and locks out operation to prevent unsafe conditions.

The two primary causes of this fault are a sticking gas valve and a fault in the flame sense circuit itself. A sticking gas valve fails to close fully when de-energized, allowing gas to continue flowing and sustaining a small flame after the burner cycle ends. Over time, gas valve internals can wear or accumulate debris, causing the valve to hang open. The flame sense circuit involves a flame sensor rod, the wiring harness connecting it to the control board, and the control board's sense input. A grounded or shorted flame sensor rod, damaged insulation on the sensor lead, or a contaminated sensor surface can all produce a false signal that mimics an actual flame being detected.

Diagnosis should begin by confirming whether gas flow actually continues after the valve should be closed, which would confirm a sticking valve. If gas flow stops correctly, inspection of the flame sensor rod and its wiring for shorts, grounding, or carbon buildup is the next logical step. A control board fault causing erroneous signal interpretation is possible but less common than the mechanical and wiring causes.

Source: manufacturer service documentation.

Common causes of 5

  1. 01

    Sticking or Faulty Gas Valve

    Part replacement

    The gas valve fails to fully close when de-energized, allowing gas to continue flowing and maintaining a small flame after the burner cycle ends. This is the most common cause and can be confirmed by listening and checking for continued gas flow after the valve should have shut.

  2. 02

    Grounded or Shorted Flame Sensor Rod

    Part replacement

    The flame sensor rod may be touching the burner housing or have cracked ceramic insulation, creating a ground path that produces a continuous false flame signal to the control board. Visual inspection of the sensor mounting and ceramic insulator will reveal this issue.

  3. 03

    Contaminated Flame Sensor Surface

    Wiring / connection

    Carbon buildup or oxidation on the flame sensor rod surface can alter its electrical characteristics and in some cases produce erratic signals interpreted as a false flame. Cleaning the rod with fine steel wool or emery cloth is the first step in ruling this out.

  4. 04

    Damaged Flame Sensor Wiring or Harness

    Part replacement

    Worn, pinched, or heat-damaged insulation on the flame sensor lead can create a short circuit that mimics a flame signal. The harness should be inspected along its full length for any damage, chafing, or contact with hot metal surfaces.

  5. 05

    Faulty Ignition Control Board

    Part replacement

    If the gas valve and flame sense circuit check out correctly, the ignition control board itself may be misinterpreting input signals and generating a false fault. This is the least common cause and should only be considered after all other components have been ruled out.

See the test procedure for each cause

Frequently asked questions about 5

What does 5 mean on a Goodman hvac?
Fault code 5 on a Goodman furnace means the ignition control is detecting a flame signal when no flame should be present, a condition called false flame sensing. This causes the control to lock out operation as a safety measure. The most common sources are a sticking gas valve that won't fully close or a problem in the flame sense circuit, such as a grounded sensor rod or damaged wiring.
Can I fix error code 5 on my Goodman furnace myself?
Some steps, like inspecting and cleaning the flame sensor rod, are within reach of a confident DIYer. However, diagnosing a sticking gas valve or tracing a wiring fault in the flame sense circuit typically requires technical experience and appropriate tools. Replacing a gas valve involves working with the gas supply line, which should be performed by a licensed technician in most jurisdictions.
Is error code 5 on a Goodman furnace a safety hazard?
The fault code itself represents the furnace's safety system working correctly by shutting down when an unexpected flame condition is detected. A sticking gas valve, if confirmed, is a serious concern because uncontrolled gas flow creates combustion and carbon monoxide risks. The system should not be bypassed or repeatedly reset without identifying and correcting the underlying cause.
How much does it cost to repair a Goodman furnace showing error code 5?
Repair costs depend on the root cause. Cleaning the flame sensor is a low-cost service call repair, generally in the range of $75 to $150 including labor. Replacing a flame sensor rod typically adds a modest parts cost on top of labor. A gas valve replacement is more involved, with parts and labor commonly ranging from $300 to $600 or more depending on the model and local labor rates.
Will resetting my Goodman furnace clear error code 5?
Resetting the furnace by cycling power may temporarily clear the fault and allow the unit to attempt operation again, but it will not resolve the underlying problem. If the sticking valve or flame sense circuit issue remains, the fault will return, often quickly. Repeated resets without repair can mask a developing problem and should be avoided until a proper diagnosis is completed.

Related Goodman hvac codes

All Goodman hvac codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass