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Vaillant Flow Switch 0020039708

Vaillant

Vaillant Flow Switch 0020039708

Vaillant flow switch 0020039708 for VU 656/4-5 and Ecotec VU 656/4-5 gas boilers.

At a glance

  • Part type: flow switch
  • Also known as 1382848
Manufacturer part no.
0020039708
Showing prices

£178.52

£148.77 ex. VAT · VAT at 20%

Available to order · 1 working day
Available to order · 1 working day
Not certain it's the right part? The technical team verifies fitment before dispatch — no charge, and it stops a second trip.Call the technical teamSend a technical question

Same-day dispatch

Ordered by 4pm Mon–Fri, 10:30am Sat.

30-day returns

Unused, in original packaging.

What it is

The Vaillant 0020039708 is a flow switch used in Vaillant gas boilers. It detects water flow through the appliance circuit and signals the control board so the boiler can respond to a demand. It is listed under gas boiler spares in the flow switch category.

Signs this part needs replacing

  • The boiler does not respond when a hot water or heating demand is present.
  • Hot water runs intermittently, cutting in and out without a clear pattern.
  • The appliance fails to fire despite water flowing through the circuit.
  • Fault symptoms appear only when flow is present, pointing to the sensing circuit rather than the pump.
  • The switch shows visible damage, contamination or a stuck internal mechanism on inspection.

Before you order

  • Confirm the boiler model against the fitment list above.
  • Check the existing part number on the component or in the manufacturer's parts list.
  • Inspect the wiring and connections to the switch before assuming the switch itself has failed.
  • Verify that the fault is flow-related and not caused by a pump, sensor or board issue.

Not sure which part?

Search by part number, product name or brand — our technical team confirms fitment before anything is dispatched.