Which speed sensor connector?

The Hall-effect sensor on Potterton Promax 33 HE uses a 4-pin JST plug. Do not swap L1/L2.

Do I need a new gasket?

Always fit the OEM Viton gasket — the old one hardens and leaks flue gases into the case.

Only if the Potterton Promax 33 HE is in warranty — Potterton require log of any part swap for labour claims.

Swap the combustion fan on Potterton Promax 33 HE when you get low-speed lockouts (F28/F29 Vaillant, EA Worcester, F1 Ideal) or bearing whine.

Remove the case, disconnect the fan plug and Venturi. Note the fan's part number stamped on the motor housing.

On Potterton Promax 33 HE the fan is torqued to 8–10 Nm — over-tightening cracks the composite plenum.

Refill the Potterton Promax 33 HE 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.

Which speed sensor connector?: The Hall-effect sensor on Potterton Promax 33 HE uses a 4-pin JST plug. Do not swap L1/L2.
Do I need a new gasket?: Always fit the OEM Viton gasket — the old one hardens and leaks flue gases into the case.
Do I need to notify the manufacturer?: Only if the Potterton Promax 33 HE is in warranty — Potterton require log of any part swap for labour claims.

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