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Error code reference

A.O. Smith Water Heater Error Code 16

No current to Power Anode (P-ANODE OPEN).

A.O. Smith codesA.O. Smith water heater codes

No current to Power Anode (P-ANODE OPEN).

First step from the service manual

Check the wire from the power anode to the upper control for damage and ensure connectors are fully seated.

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

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What 16 means on a A.O. Smith water heater

Error code 16 on an A.O. Smith water heater indicates an open circuit condition in the power anode circuit. The power anode (P-ANODE) is an electrically powered sacrificial anode rod that actively protects the tank lining from corrosion, unlike passive magnesium or aluminum anodes. The upper control board monitors current flow through the power anode continuously. When no current is detected on that circuit, the control triggers error code 16 to alert the technician that the protective anode system is not functioning.

The most common cause of this fault is a wiring failure between the power anode and the upper control board. This includes broken wire strands, chafed insulation causing an open, or connector pins that have backed out or corroded. The diagnostic process begins by tracing the wire from the power anode connection point up to the upper control board, checking for visible damage, pinched sections, or loose connectors that need to be fully seated.

If the wiring and connectors check out, the power anode itself may have failed internally, creating the open circuit condition. A failed anode will not pass current and will register as an open on the control board. In some cases, the upper control board itself may have a faulty input circuit for the anode, though this is a less common cause. Resolving this fault promptly is important because the tank lacks active corrosion protection while error code 16 is active.

Source: manufacturer service documentation.

Common causes of 16

  1. 01

    Loose or unseated wiring connector

    Wiring / connection

    The connector linking the power anode wire to the upper control board may have vibrated loose or was never fully seated. Inspect the connector at both ends and press firmly until it clicks into place.

  2. 02

    Damaged or broken wire

    Part replacement

    The wire running from the power anode to the upper control can break internally or suffer chafing damage from contact with the tank or plumbing. Trace the full length of the wire and look for cuts, kinks, or bare spots.

  3. 03

    Corroded or damaged connector pins

    Part replacement

    Connector pins exposed to moisture or heat cycles can corrode or deform, breaking the electrical path even when the connector appears seated. Inspect the pins visually and check for continuity across the connector.

  4. 04

    Failed power anode

    Part replacement

    The power anode rod itself can fail internally, creating an open circuit that the control board detects as no current flow. If wiring checks out, the anode should be tested for continuity and replaced if it reads open.

  5. 05

    Faulty upper control board

    Part replacement

    If the wiring and power anode both test good, the input circuit on the upper control board that monitors anode current may have failed. This is the least likely cause and should be diagnosed only after all other components have been ruled out.

See the test procedure for each cause

Frequently asked questions about 16

What does 16 mean on a A.O. Smith water_heater?
Error code 16 means the upper control board is detecting no current flowing through the power anode circuit, a condition called P-ANODE OPEN. This tells the control that the powered sacrificial anode rod is not functioning electrically. The fault is most often caused by a loose connector or a damaged wire between the power anode and the upper control board.
How do I fix error code 16 on my A.O. Smith water heater?
Start by inspecting the wire that runs from the power anode to the upper control board for any visible damage, and check that all connectors are fully and firmly seated. If the wiring looks intact, test the power anode itself for continuity to determine whether it has failed internally. Replace any damaged wiring, connectors, or the anode rod as needed based on your findings.
Will resetting the water heater clear error code 16?
A simple reset will not permanently clear error code 16 because the control board will re-detect the open circuit in the power anode as soon as it checks the circuit again. The underlying wiring fault or component failure must be repaired before the code will stay cleared. Resetting can be useful to confirm the repair was successful after the fix is made.
Is it safe to continue using my water heater with error code 16 active?
The water heater may continue to heat water with code 16 active, but the power anode is not providing corrosion protection to the tank interior while this fault is present. Running the unit without active anode protection for an extended period can accelerate tank corrosion and shorten the life of the water heater. It is best to diagnose and repair the fault as soon as possible.
How much does it cost to repair error code 16 on an A.O. Smith water heater?
If the fix is simply reseating a loose connector, there may be no parts cost at all, just labor time. Replacing a damaged wire or connector typically falls in the range of $50 to $150 in parts and labor depending on the extent of the damage. A failed power anode rod replacement or a control board replacement will cost more, generally ranging from $150 to $400 or higher depending on parts pricing and local labor rates.

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