De Dietrich S101725 Q45 fan

The De Dietrich S101725 Q45 fan is listed under catalogue article 375.145.055 in the Fans and Flue Gas Exhausters category. Parts of this type supply combustion air to the burner and, in room-sealed appliances, also expel flue gases. In modulating premix boilers, the fan speed determines the firing rate: the burner control varies the fan speed, and the gas valve follows proportionally. This makes the fan a central component in the air‑gas ratio control loop. When selecting a replacement fan of this class, the key parameters are air flow and pressure at the required operating point, the orientation of the outlet (rotational position), the impeller diameter, the supply voltage and control mode (e.g., mains‑driven, PWM, 0–10 V), and the flange pattern that mates with the burner or boiler casing. Common failure modes in fans of this type include worn bearings, imbalance caused by debris or scale deposits on the impeller, a failed run capacitor (where applicable), and speed‑feedback errors that the boiler control interprets as an airflow fault, leading to a lockout. When replacing an existing fan, verify that the mounting flange, outlet direction, and electrical connections match the original, and check that the air pressure switch remains correctly set for the new fan’s performance curve.