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Washer Leak sensor and AquaStop: What It Does and Signs It's Failing

Bosch washers with AquaStop have a base tray under the machine with a float switch in it. When water collects in the tray, the float trips and the valve at the faucet end of the AquaStop hose shuts the water off. The washer then shows a leak code.

How it works

The float lifts a switch once there's enough water in the tray, and the control goes into leak mode. The water itself comes from somewhere above: a split internal hose, a leaking seal or the supply hose.

Signs it is failing

• Leak or AquaStop code
• Washer won't fill
• Water under or around the machine
• Code comes straight back after a reset

Leak and AquaStop codes come from this float. The real fix is finding the leak above it.

Can you replace it yourself?

Turn the water off at the faucet and unplug the washer as soon as you see a leak code. Bosch says to stop using the machine and call service. Don't tip the washer to drain the tray or try to defeat the float, because it's what stops a flood.

Buying the right part

The tech will order the hose, seal or sensor by full model number. AquaStop hoses are model-specific.

Error codes linked to the leak sensor and aquastop

• E23 / F23Leak detected or AquaStop triggeredBosch

Last reviewed 2026-10-19.