Combined or separate?

Vaillant ecoFIT Pure 435 runs a two-electrode kit — one spark, one sense. Fit both together to avoid a second call-back.

How do I test ionisation current?

In service mode read the µA value on Vaillant ecoFIT Pure 435. Below 4 µA at steady state means clean or replace.

Only if the Vaillant ecoFIT Pure 435 is in warranty — Vaillant require log of any part swap for labour claims.

Renew the ignition and flame-sense electrodes on Vaillant ecoFIT Pure 435 when you get F27 / EA / L2 flame-detection faults after a clean burn.

Both electrodes on Vaillant ecoFIT Pure 435 use ceramic insulators — never re-use if chipped.

Set the spark gap to 3.5–4.0 mm and the ionisation gap so the tip sits 4–5 mm above the burner surface.

Refill the Vaillant ecoFIT Pure 435 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.

Combined or separate?: Vaillant ecoFIT Pure 435 runs a two-electrode kit — one spark, one sense. Fit both together to avoid a second call-back.
How do I test ionisation current?: In service mode read the µA value on Vaillant ecoFIT Pure 435. Below 4 µA at steady state means clean or replace.
Do I need to notify the manufacturer?: Only if the Vaillant ecoFIT Pure 435 is in warranty — Vaillant require log of any part swap for labour claims.

Shop the spares

Browse boiler spares — 14,820 live parts.