Inspect annually at service; replace at 5-year mark or after any freeze event.

No — use OEM only; the seal geometry on Vaillant ecoFIT Pure 425 varies between production years.

Do I need to notify the manufacturer?

Only if the Vaillant ecoFIT Pure 425 is in warranty — Vaillant require log of any part swap for labour claims.

How to Replace the Siphon Trap on a Vaillant ecoFIT Pure 425 (UK)

Replace the condensate siphon on Vaillant ecoFIT Pure 425 for D5 / F1 pressure faults after a hard frost or heavy servicing schedule.

Isolate, drop the case front. Undo the siphon quick-release clip on Vaillant ecoFIT Pure 425, tip out old fluid.

Prime the new siphon with 250 mL clean water before refitting — dry siphons throw immediate flue-pressure faults.

Refill the Vaillant ecoFIT Pure 425 to 1.2 bar cold. Bleed high-point radiators and the internal AAV.

Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.

Interval?: Inspect annually at service; replace at 5-year mark or after any freeze event.
Can I fit generic?: No — use OEM only; the seal geometry on Vaillant ecoFIT Pure 425 varies between production years.
Do I need to notify the manufacturer?: Only if the Vaillant ecoFIT Pure 425 is in warranty — Vaillant require log of any part swap for labour claims.

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