Flow Sensor

Flow sensor 405942 is a magnetic switch with a 0.7m PVC cable terminated with flat (faston) connectors, forming a safety component of the combustion system in the Kranzle therm series pressure washer. The sensor detects the flow of working water and sends an electrical signal to the control circuit – the heating burner can only be activated when the sensor confirms flow. Absence of flow with the pump running (e.g. gun closed, blocked filter, insufficient water supply) blocks ignition and protects the heating system from running dry.

Application

The sensor is mounted in the hydraulic circuit of the therm washer – on the working water path where it can detect water movement. The magnetic switch responds to a ferromagnetic element (float or rotor) moving in the flow channel under the influence of flowing water – movement of this element changes the magnetic field at the switch and causes it to switch state. The 0.7m PVC cable with flat connectors links the switch to the control board or directly to the burner control circuit.

Replaced when the burner fails to ignite despite correct water flow, when the burner activates irregularly, or after an open circuit is identified in the sensor's electrical circuit.

Symptoms – when to replace

• Burner does not ignite despite correct water flow and an intact ignition system – the sensor does not send a signal despite actual flow.
• Burner switches on and off irregularly with no changes to gun operation or flow – intermittent contact in the switch or a damaged cable at the connector.
• Burner does not shut off after the gun is closed – the sensor reports flow despite its absence (switch locked in the closed position).
• Visible mechanical damage to the PVC cable – chafing, burning or deformation at the faston connector.
• No circuit continuity when measured with a multimeter between the connectors with confirmed flow through the sensor.

How to select the right part

Identify by reference number 405942. Flow sensors differ in switch type, cable length, connector type and mounting geometry – a replacement with a different cable length or connector type may not fit without wiring modification. The 0.7m cable length and flat (faston) connectors are identifying parameters: confirm they match the removed component before ordering.

When diagnosing before replacement: check circuit continuity between the sensor connectors with a multimeter – with the gun open (flow) and closed (no flow). A correctly functioning magnetic sensor switches state during flow. No switching despite flow indicates a damaged switch. A constant signal regardless of flow indicates a blocked mechanism in the flow channel, not necessarily a damaged switch.

Compatibility

Component of the combustion system in Kranzle therm series pressure washers. Verify the exact compatibility range by reference number 405942 and the therm washer model.

[faq]

How to check whether the flow sensor is the cause of ignition failure before replacing it?|Connect a multimeter to the sensor cable connectors in continuity or resistance measurement mode. Start the washer with the gun open – with water flowing, the switch should change state (close or open the circuit, depending on the design). If the circuit state does not change despite clear flow, the sensor is not working correctly. If it switches correctly on direct measurement but the burner still does not operate – look for the cause in the wiring, control board or ignition system, not the sensor itself.

What are the risks of operating a therm washer with a damaged flow sensor – can this safety feature be temporarily bypassed?|The flow sensor is a safety component, not a convenience feature – bypassing it or permanently shorting the circuit would allow the burner to ignite without water flow. The result could be overheating of the heat exchanger, damage to seals and pipes in the heating system, or in extreme cases activation of the safety valve following a sudden pressure surge. Do not operate a therm washer with the flow sensor bypassed – replacing 405942 is the only correct solution for a damaged sensor.

How long does the 0.7m PVC cable last in the therm washer environment – is corrosion of the faston connectors a typical problem?|Flat faston connectors in a moist environment with varying temperatures corrode over time – particularly without adequate protection from direct water spray. Typical ageing symptoms are green deposits on the contacts, increased connection resistance and intermittent contact during pump vibration. At every therm washer service, check the sensor connector condition – wipe the contacts with a dry cloth and assess the degree of corrosion. Contacts can be cleaned with electrical contact cleaner. If corrosion is deep or contacts are mechanically deformed, replacing the connectors alone without the full cable may be insufficient.

Is flow sensor 405942 the same component as the pressure switch (TS microswitch) of the Total Stop system?|No – these are two different components with different functions. Flow sensor 405942 is a magnetic switch responding to the mechanical movement of an element driven by flowing water – its signal concerns the fact of flow and serves the combustion system. The Total Stop microswitch (Mikroschalter 15.018) responds to hydraulic pressure in the circuit – its signal concerns pressure level and serves to stop the motor when the gun is closed. Both operate independently and neither can substitute for the other.

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