Oil storage and supply: distinguish head, restriction and air ingress
Follow the oil path from storage to the fuel unit and, where the arrangement uses one, back through the return. Storage is part of the working heating system, not merely an inventory container. The tank, support, connections, fill arrangement and vent must remain suitable for the installation. A blocked vent can create a filling hazard, and an abandoned fill pipe can mislead a delivery unless the required closure and identification process is completed. A gauge reading alone does not prove usable clean fuel is reaching the burner.
Inspect the fuel condition and the pressure boundary. Water can collect at low points and contribute to corrosion or delivery problems. Sediment disturbed by a delivery can reach filters, while contamination at an oil-water interface can support deposits. Fuel blends and seal materials must be compatible with the equipment’s approval. A gasket that looks similar or a fitting with matching threads can still be unsuitable. Keep open lines and new components clean, using the specified joining and protection methods.
Separate static elevation effects from friction under flow. A liquid surface above the pump can supply positive static head; a pump drawing from below must overcome lift as well as line resistance. A longer or more restrictive suction path generally requires greater vacuum for comparable delivery. Colder viscous oil can change those conditions. Where a gauge is connected matters: a reading downstream of a filter includes a pressure loss that an upstream reading may not include. Use known test points and the actual operating flow when comparing evidence.
A suction leak does not always produce a visible outward drip. When the line is below atmospheric pressure, air can enter through a defect. This can explain loss of prime or unstable delivery after a long off cycle, but the complete arrangement must still be checked. A recent filter service makes disturbed gaskets and covers relevant, not automatically guilty.
Understand the fuel unit’s configuration. One-pipe and two-pipe arrangements can require different internal bypass provisions, and a required return must not be accidentally blocked. Circulating flow through a two-pipe supply may exceed the nozzle’s consumption. Do not improvise an arrangement from a diagram for another pump. Match rotation, drive, pressure and suction capabilities to the manufacturer’s requirements, then verify both operation and containment after the work.