Réchauffeur d'alimentation en carburant défectueux

The heater warming diesel before it reaches the filter or the pump, faulty so cold fuel is delivered unheated. Diesel forms wax crystals as it cools — the cloud point — and those crystals block a filter completely. The heater exists to keep fuel above that temperature, and it only matters when it is cold.

So the fault is seasonal and looks like fuel starvation. Loss of power, stalling and a no-start on a frosty morning, clearing entirely once the day warms or the engine's own returning fuel has warmed the tank. A vehicle that runs perfectly from mid-morning and fails at dawn is describing wax, not a pump.

Check the heater's supply before its element. These circuits draw significant current and are switched by a relay on a temperature threshold, so a relay that never closes leaves a perfect element cold. Winter-grade fuel matters as much as the heater — fuel bought in a mild spell and used in a cold one will wax whatever the heater does, and an additive is the immediate remedy while the heater is diagnosed.