Do I need to gas-tighten test?

Yes — a soundness test and let-by test is mandatory before recommissioning.

Most Vaillant ecoFIT Pure 425 gas valve inlets are ½" BSP, 24 mm across flats; use two spanners to avoid rotating the manifold.

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.

Change the modulating gas valve on Vaillant ecoFIT Pure 425 for hard ignition, F27 flame-lift or repeated flame loss faults.

Cap the gas at the isolator, disconnect the multi-pin harness and undo the gas valve union. Fit a new fibre washer.

Perform a full gas rate and combustion analysis after fitting the Vaillant ecoFIT Pure 425 valve — CO/CO2 ratio must fall inside the OEM window.

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.

Do I need to gas-tighten test?: Yes — a soundness test and let-by test is mandatory before recommissioning.
Which spanner size?: Most Vaillant ecoFIT Pure 425 gas valve inlets are ½" BSP, 24 mm across flats; use two spanners to avoid rotating the manifold.
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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