Bradford White Water Heater Error Code 4

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.

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.

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.

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.

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.