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Error code reference

Coleman Furnace Error Code 5 FLASH

Gas flow detected with no call for heat.

Coleman codesColeman furnace codes

Gas flow detected with no call for heat.

First step from the service manual

Check gas valve and gas valve wiring.

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

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  • Wiring diagram references and connector pinouts from the OEM service manual
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What 5 FLASH means on a Coleman furnace

The 5 FLASH error code on a Coleman furnace indicates that the control board has detected gas flow through the system when no call for heat is present. This is a safety-critical fault. The furnace's control board continuously monitors the gas valve circuit and flame sensor signals. When it detects gas flowing or a flame signal during a period when the thermostat has not initiated a heating cycle, it triggers this lockout to prevent uncontrolled combustion or gas accumulation.

The most likely hardware cause is a faulty gas valve that is leaking gas through the valve seat or has a shorted solenoid coil that allows the valve to open without a command signal from the control board. Wiring issues are also a common culprit, including a short circuit in the gas valve wiring harness that sends a false 24VAC signal to the valve solenoid. A contaminated or failed flame sensor that produces a spurious flame signal can also trigger this code, as can a control board that is incorrectly reading feedback from the valve circuit.

Diagnosing this fault begins with inspecting the gas valve and its wiring for visible damage, shorts, or loose connections. Using a multimeter, a technician should verify that 24VAC is not present at the gas valve terminals when no call for heat is active. If voltage is present without a thermostat demand, the source of that rogue signal, either the wiring or the control board, must be identified. If no voltage is present but the fault persists, the gas valve itself may be leaking through mechanically and should be tested or replaced.

Source: manufacturer service documentation.

Common causes of 5 FLASH

  1. 01

    Faulty gas valve

    Part replacement

    The gas valve may be stuck open or leaking through its seat, allowing gas to pass without a command signal. This can also occur if the valve solenoid coil is internally shorted, causing it to open without receiving a proper 24VAC signal.

  2. 02

    Short circuit in gas valve wiring

    Wiring / connection

    A short in the wiring harness between the control board and the gas valve can apply voltage to the valve solenoid unintentionally. Inspect the wiring for pinched insulation, chafed wires, or connections that are contacting the furnace cabinet.

  3. 03

    Failed control board

    Part replacement

    If the control board has a failed relay or internal component, it may send a continuous voltage signal to the gas valve even when no heat call is present. This is identified after ruling out wiring faults and a defective gas valve.

  4. 04

    Contaminated or failed flame sensor

    Wiring / connection

    A flame sensor that is coated with residue or is failing electrically can produce a spurious signal that the control board interprets as a flame present without a call for heat. The sensor rod should be inspected and cleaned or replaced.

  5. 05

    Incorrect wiring after service

    Wiring / connection

    If the furnace was recently serviced, wires may have been incorrectly reconnected at the gas valve terminals. Verify that all wiring matches the correct terminal designations on both the valve and the control board.

See the test procedure for each cause

Frequently asked questions about 5 FLASH

What does 5 FLASH mean on a Coleman furnace?
A 5 FLASH error on a Coleman furnace means the control board has detected gas flow or a flame signal when the thermostat has not made a call for heat. This is a safety lockout condition designed to prevent uncontrolled gas combustion. The furnace will not operate until the underlying cause is diagnosed and corrected. The first components to inspect are the gas valve and its associated wiring.
Is a 5 FLASH error on a Coleman furnace a safety hazard?
Yes, this fault should be treated as a safety concern. Gas flowing without a call for heat can indicate a gas valve that is stuck open or a wiring fault creating an unintended circuit. If you suspect gas is actively leaking into your home, turn off the gas supply to the furnace, ventilate the area, and contact a qualified technician before attempting any diagnostics.
Will resetting my Coleman furnace clear the 5 FLASH error?
A power reset may temporarily clear the fault code and allow the furnace to attempt operation again, but it will not resolve the underlying problem. If the gas valve, wiring, or control board issue that caused the 5 FLASH fault is still present, the error will return. The fault must be properly diagnosed and repaired to prevent recurrence.
Can I fix a 5 FLASH error on my Coleman furnace myself?
Some steps, such as inspecting the gas valve wiring for visible shorts or loose connections, can be performed by a knowledgeable DIYer with the power and gas supply off. However, diagnosing a leaking gas valve or a failed control board requires a multimeter and familiarity with gas appliance safety procedures. Because this code involves gas flow, it is strongly recommended to have a qualified HVAC technician complete the repair if you are not experienced with gas furnace service.
How much does it cost to repair a Coleman furnace showing a 5 FLASH error?
Repair costs vary depending on the faulty component. A gas valve replacement typically ranges from $150 to $400 including parts and labor. Control board replacement can range from $200 to $600 or more depending on the board. If the fix involves only a wiring repair, costs are generally lower, often in the $75 to $200 range for a service call and labor. Obtaining a diagnosis before authorizing parts replacement is always advisable.

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