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Error code reference

Bradford White Water Heater Error Code 4

Low flame sense current.

Bradford White codesBradford White water heater codes

Low flame sense current.

First step from the service manual

Check flame sensor for deposits; verify flame sense current is adequate (minimum 1 microamp, typical 5-30 microamps).

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

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What 4 means on a Bradford White water heater

Error code 4 on a Bradford White water heater indicates low flame sense current. The flame sensor, also called a flame rod, works by passing a small electrical current through the burner flame to confirm ignition has occurred. When the control board detects that the microamp signal returning from the flame sensor falls below the minimum acceptable threshold of 1 microamp, it logs this fault and may shut down the burner to prevent unsafe operation. Under normal conditions, a healthy flame sensor reading should fall between 5 and 30 microamps.

The most common reason for a low flame sense reading is contamination on the flame sensor rod itself. Over time, the rod can accumulate a coating of oxidation, carbon deposits, or mineral residue that acts as an insulator and reduces the current signal. The sensor tip sits directly in the burner flame path, making it vulnerable to fouling from combustion byproducts. Even a thin layer of buildup is enough to drop the signal below the usable range.

Beyond sensor contamination, electrical issues in the flame sense circuit can also trigger this code. A cracked ceramic insulator on the sensor rod, a damaged or corroded wire connection between the sensor and the control board, or a deteriorating control board itself can all cause the microamp reading to drop artificially. In some cases, a weak or improperly positioned flame caused by a partially blocked burner orifice or low gas pressure will also produce insufficient flame sense current even with a clean sensor.

Source: manufacturer service documentation.

Common causes of 4

  1. 01

    Contaminated flame sensor rod

    Wiring / connection

    Oxidation, carbon buildup, or mineral deposits on the sensor tip insulate the rod and reduce the microamp signal below the 1 microamp minimum. Inspect the rod tip for discoloration or a white, gray, or black coating and clean it with fine steel wool or emery cloth.

  2. 02

    Damaged or corroded flame sensor wiring

    Wiring / connection

    The wire connecting the flame sensor to the control board can develop corrosion at the terminals or physical damage along its length, interrupting the flame sense circuit. Inspect the connector and wire for discoloration, fraying, or looseness.

  3. 03

    Failed flame sensor rod

    Part replacement

    If cleaning does not restore the signal to the 5 to 30 microamp typical range, the sensor rod itself may be cracked or the ceramic insulator may have deteriorated, requiring replacement of the component.

  4. 04

    Weak or improperly positioned flame

    Wiring / connection

    A partially blocked burner orifice, low gas pressure, or incorrect air-to-gas mixture can produce a flame too small or too far from the sensor tip to generate adequate current. Check the burner flame visually and verify gas supply pressure is within specification.

  5. 05

    Faulty control board

    Part replacement

    If the flame sensor, wiring, and burner flame all check out correctly but the fault persists, the control board's flame sense input circuit may have failed and is misreading the signal. This requires board replacement.

See the test procedure for each cause

Frequently asked questions about 4

What does 4 mean on a Bradford White water_heater?
Error code 4 on a Bradford White water heater means the control board is detecting low flame sense current from the flame sensor. The sensor must read at least 1 microamp to confirm a valid flame, with normal operation producing 5 to 30 microamps. When the signal falls below that threshold, the unit logs this fault and may cycle the burner off as a safety measure. The most frequent cause is a dirty or oxidized flame sensor rod.
How do I fix error code 4 on my Bradford White water heater?
Start by locating the flame sensor rod in the burner assembly and inspecting its tip for deposits or discoloration. Cleaning the rod with fine steel wool or emery cloth to remove oxidation or carbon buildup often restores the signal without any parts needed. If cleaning does not resolve the fault, check all wiring connections between the sensor and the control board for corrosion or damage. If those components are intact, the sensor rod or control board may need to be replaced.
Is error code 4 on a Bradford White water heater a safety hazard?
Error code 4 is a protective fault, meaning the heater is designed to detect this condition and respond safely. The control board uses the flame sense signal to confirm that combustion is actually occurring, and a low reading causes it to shut down the burner rather than allow an uncontrolled situation. While the fault itself is not an immediate danger, you should address it promptly because the heater may not reliably produce hot water and repeated failed ignition attempts can stress other components.
Will resetting my Bradford White water heater clear error code 4?
A manual reset may temporarily clear the fault and allow the heater to attempt ignition again, but if the underlying cause is not corrected the code will return. The control board detects the low flame sense current each time the burner fires, so a dirty sensor or damaged wiring will continue triggering the fault. A reset is useful as a first step to confirm the issue, but cleaning or replacing the faulty component is necessary for a lasting fix.
How much does it cost to repair error code 4 on a Bradford White water heater?
If the fix is simply cleaning the flame sensor rod, there is no parts cost and the repair can often be completed in under an hour. If the flame sensor rod needs replacement, parts typically range from $15 to $50 depending on the specific unit. A control board replacement is the most expensive scenario, with parts and labor potentially totaling $200 to $500 or more. Having a technician diagnose the fault first can help avoid replacing parts unnecessarily.

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