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Error code reference

Zenith Dishwasher Error Code F18

No water in tub (turbidity based)

Zenith codesZenith dishwasher codes

No water in tub (turbidity based) - Water not detected by turbidity sensor.

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What F18 means on a Zenith dishwasher

The F18 error code on a Zenith dishwasher indicates that the control system has not detected water in the wash tub, with the detection method being turbidity-based rather than a simple float switch or pressure sensor. The turbidity sensor works by measuring the optical clarity or particulate density of water passing through it. When the dishwasher fills, the sensor should register the presence of water. If it does not detect this within the expected timeframe, the F18 code is triggered and the cycle is halted as a protective measure to prevent the wash pump from running dry.

The turbidity sensor itself is typically located in the sump area at the bottom of the tub. It uses an infrared LED and photodetector pair to measure water clarity. If water is absent, the sensor receives an unobstructed light signal and reports a no-water condition. However, the same result can occur if the sensor is heavily fouled with grease or mineral deposits, since buildup can interfere with the optical path and produce a false reading even when water is present in the tub.

Beyond the sensor itself, F18 can also point to upstream fill problems. A faulty water inlet valve, low household water pressure, a kinked supply hose, or a clogged inlet screen can all prevent adequate water from entering the tub. In these cases, the turbidity sensor is reporting accurately, but the root cause is a fill system failure rather than a sensor fault. Systematic diagnosis should address both the fill path and the sensor condition before replacing components.

Source: manufacturer service documentation.

Common causes of F18

  1. 01

    Clogged or fouled turbidity sensor

    Wiring / connection

    Grease, mineral scale, or food debris coating the turbidity sensor's optical lens can block its ability to detect water correctly. Inspect the sensor in the sump area and clean the lens surface carefully with a soft cloth.

  2. 02

    Faulty or closed water inlet valve

    Part replacement

    The water inlet valve may be defective, receiving insufficient voltage, or blocked by debris at its inlet screen. Check that the valve opens during the fill cycle and that the inlet screen is clear of sediment.

  3. 03

    Low household water pressure

    Wiring / connection

    The dishwasher requires adequate incoming water pressure to fill within the expected time window. If pressure is too low, the tub may not fill fast enough for the sensor to register water before the control times out.

  4. 04

    Kinked or blocked water supply hose

    Wiring / connection

    A kinked supply hose behind or beneath the unit can restrict or completely stop water flow into the tub. Pull the dishwasher out slightly and inspect the hose along its full length for bends or crushing.

  5. 05

    Defective turbidity sensor

    Part replacement

    If cleaning the sensor does not resolve the code and the fill system is confirmed functional, the turbidity sensor itself may have an internal failure. A faulty sensor will need to be replaced to restore accurate water detection.

See the test procedure for each cause

Frequently asked questions about F18

What does F18 mean on a Zenith dishwasher?
F18 on a Zenith dishwasher means the turbidity sensor did not detect water in the wash tub during the fill phase. The dishwasher uses this sensor to confirm water is present before starting the wash pump. The cycle stops automatically to protect internal components from running dry. The cause may be a fill system problem, a dirty sensor, or a faulty sensor.
Can I fix the F18 error myself without calling a technician?
In many cases, yes. Start by checking that the water supply valve behind or under the dishwasher is fully open and the supply hose is not kinked. Then inspect and clean the turbidity sensor in the sump area, removing any grease or mineral buildup from its lens. If those steps do not resolve the code, further diagnosis of the inlet valve or sensor replacement may require a technician.
Will resetting the dishwasher clear the F18 code?
A reset may temporarily clear the F18 code, but if the underlying cause is not corrected, the code will return as soon as the next fill cycle runs. Use a reset only after you have addressed the root cause, such as cleaning the sensor or restoring proper water flow. Repeated resets without repairs will not resolve the issue.
Is it safe to use my Zenith dishwasher while the F18 code is active?
No. The F18 code stops the cycle specifically to prevent the wash pump from running without water, which can cause serious mechanical damage. You should not attempt to force the dishwasher through a cycle while this error is present. Address the water supply or sensor issue before running the appliance again.
How much does it cost to repair an F18 error on a Zenith dishwasher?
Repair costs depend on the root cause. Cleaning a fouled turbidity sensor costs nothing beyond your time. Replacing a defective water inlet valve or turbidity sensor typically involves parts costs ranging from $20 to $80 depending on the component, plus labor if a technician is hired. A full service call with diagnosis and repair generally runs between $100 and $250.

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