Magnetic switch for Therm flow sensor

The magnetic switch for the Therm flow sensor is a component cooperating with the flow-detection system in Therm-series heated washers. In service practice, it provides the control system (heating/safety logic) with a signal that flow conditions are met. A faulty switch can cause heating start issues or unstable heater operation.

MPN / reference: 405942

APPLICATION

The part is used in typical service work on heated washers:

• repairing the flow sensor system in Therm machines,
• restoring correct operation of the flow-detection circuit,
• diagnosing and fixing heating start-up problems,
• servicing safety logic that requires confirmed flow to allow heating.

SYMPTOMS - WHEN IT’S WORTH REPLACING

Consider replacing the switch when you notice:

• heating does not start despite correct water flow,
• heating starts and shuts off irregularly,
• the machine enters a safety/protection mode related to flow detection,
• fault confirmed by electrical diagnostics (no switching/intermittent contact),
• damage to wiring, connector, or the housing.

HOW TO CHOOSE THE RIGHT PART

Selection should be unambiguous:

• confirm the part is for the Therm flow sensor,
• verify the manufacturer number: MPN 405942,
• compare the design and connector with the removed part,
• base selection on the machine’s service documentation.

For heating control components, correct version and connection method are critical - a “similar” switch can behave differently in the controller logic.

COMPATIBILITY

Select the switch based on MPN 405942 and compatibility with the specific flow sensor in the Therm machine. The safest confirmation is the parts list and comparison with the removed component.

[faq]

Is the magnetic switch the same as the flow sensor itself?|No. It’s a component that works with the flow sensor and provides the “signal” to the controller. Depending on design, the flow sensor may have a hydraulic part (flow) and a signal part (switch).

What symptoms point to a flow-signal issue rather than the burner or fuel system?|If heating doesn’t even attempt to run while cold-water operation is normal, and the controller requires flow confirmation, suspicion often falls on the flow sensor/switch. Electrical diagnostics is the final confirmation.

Can contamination in the system cause symptoms that look like a faulty switch?|Yes. If the hydraulic part of the flow sensor is dirty or moves stiffly, the switch may not be activated despite flow being present. That’s why both the hydraulic and signal sides should be checked.

Can I use a different switch if the plug fits?|Not recommended. Differences may include switching characteristics and how it matches the controller logic. The safest selection is by MPN 405942.

What should I check after replacing the magnetic switch?|Verify wiring/connector integrity, confirm stable signal during operation (heating starts and runs without interruptions), and check that the hydraulic side of the flow sensor isn’t causing activation issues.

[/faq]