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Error code reference

Bosch Water Heater Error Code EC

Gas leakage error, gas valve circuit not closing properly.

Bosch codesBosch water heater codes

Gas leakage error, gas valve circuit not closing properly.

First step from the service manual

Disconnect power supply cord and check wire connections on gas valve and the two connectors on the control board.

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

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What EC means on a Bosch water heater

The EC error code on a Bosch water heater indicates a gas leakage error, specifically a condition where the gas valve circuit is not closing properly. This means the control board has detected that the gas valve is not seating or deenergizing as expected during or after a heating cycle. The gas valve is a safety-critical component that must open to allow gas flow during ignition and close completely when the burner is not needed. When the circuit controlling this valve fails to confirm a proper closed state, the unit locks out and displays EC to prevent uncontrolled gas flow.

The gas valve on a Bosch water heater is operated through a dedicated electrical circuit connecting the valve solenoid to the control board via two specific connectors. If any part of this wiring path develops a loose connection, corrosion, or a short, the control board cannot reliably read the valve's operating state. This circuit failure can mimic the electrical signature of a valve that is not fully closing, triggering the gas leakage error even if the physical valve itself is functioning correctly.

The first diagnostic step is to disconnect the power supply cord before inspecting anything. Once power is removed, technicians should carefully check the wire connections directly on the gas valve body and trace both connectors back to the control board, looking for loose pins, corroded terminals, or damaged insulation. If wiring checks out clean and secure, the gas valve itself or the control board may need further evaluation, as either can be the source of the faulty circuit signal.

Source: manufacturer service documentation.

Common causes of EC

  1. 01

    Loose or disconnected wiring at the gas valve

    Wiring / connection

    The connectors at the gas valve body can work loose over time due to vibration or heat cycling. A loose pin or unseated connector will break the circuit continuity the control board needs to confirm the valve is closing properly.

  2. 02

    Corroded or damaged connector pins at the control board

    Wiring / connection

    The two connectors on the control board that link to the gas valve circuit are prone to oxidation or physical damage. Inspect each pin for discoloration, bent contacts, or moisture intrusion that could cause an intermittent or failed circuit.

  3. 03

    Faulty gas valve solenoid

    Part replacement

    If the solenoid coil inside the gas valve has failed or developed a short, the control board will read an abnormal circuit state and trigger the EC code. The valve would need to be tested for proper resistance and replaced if out of specification.

  4. 04

    Failed or damaged wiring harness

    Part replacement

    The wiring between the gas valve and control board can develop breaks, shorts, or melted insulation due to heat exposure near the burner assembly. Visually inspect the full length of the harness for any damage.

  5. 05

    Defective control board

    Part replacement

    If the wiring and gas valve both check out correctly, the control board itself may have a failed output relay or damaged circuit responsible for monitoring the valve. A faulty board will produce false EC readings even when all downstream components are functional.

See the test procedure for each cause

Frequently asked questions about EC

What does EC mean on a Bosch water_heater?
EC on a Bosch water heater indicates a gas leakage error caused by the gas valve circuit not closing properly. The control board has detected that it cannot confirm the gas valve is fully shutting off, so the unit locks out as a safety measure. This code requires inspection of the gas valve wiring and control board connectors before the unit can safely resume operation.
Is the EC error code on a Bosch water heater dangerous?
The EC code is a serious safety alert because it relates to the gas valve not closing as expected. The unit shuts itself down specifically to prevent uncontrolled gas flow. You should not attempt to override the lockout or bypass the error. Disconnect power, ventilate the area if you smell gas, and address the underlying wiring or component issue before restarting the unit.
Will resetting the Bosch water heater clear the EC error code?
A simple reset may temporarily clear the EC code, but the error will return if the underlying cause has not been resolved. Because this code is tied to a safety-critical gas valve circuit, a reset without a proper diagnosis and repair is not a lasting or safe solution. The wiring connections and gas valve circuit should be inspected and confirmed secure before relying on the unit again.
How do I fix the EC error code on a Bosch water heater?
Start by disconnecting the power supply cord completely. Then inspect all wire connections directly on the gas valve and trace both connectors to the control board, checking for loose, corroded, or damaged terminals. If the wiring is intact and secure, further testing of the gas valve solenoid and control board will be needed to identify which component is at fault. A qualified technician should handle gas valve replacement or control board evaluation.
How much does it cost to repair an EC error code on a Bosch water heater?
Repair costs vary depending on the root cause. If the fix is simply reseating a loose connector, the cost may be limited to a service call fee, typically in the range of $75 to $150. If the gas valve needs replacement, parts and labor combined can range from $200 to $500 or more. A control board replacement generally falls in a similar or higher range depending on the model and labor rates in your area.

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