Descale up to 15% flow loss; replace beyond. Sentinel R200 works but takes 4 hours.

Vaillant ecoFIT Pure 425 uses a 10-plate or 14-plate HEX depending on rating — cross-check the model suffix.

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 Dhw Heat Exchanger on a Vaillant ecoFIT Pure 425 (UK)

Fit a new plate HEX on Vaillant ecoFIT Pure 425 when DHW runs lukewarm but CH temperatures are correct — classic scaled plate symptom.

Isolate mains cold and CH, remove the four Allen bolts and lift the plate HEX from the hydraulic block on Vaillant ecoFIT Pure 425.

Fit new O-rings and grease with silicone; never re-use the old seals.

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.

Descale or replace?: Descale up to 15% flow loss; replace beyond. Sentinel R200 works but takes 4 hours.
Plate count?: Vaillant ecoFIT Pure 425 uses a 10-plate or 14-plate HEX depending on rating — cross-check the model suffix.
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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