How to Tell if There Is Water in Heating Oil

Written by mike smith
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Water present in your heating oil can be damaging to your furnace and heating oil filters, so it is important to make sure the heating oil held in the tank is as clean as possible. Even if your tank is securely underground, water may be inside because of condensation. Even if your heating oil tank has no functional problem, water can be introduced to the system in delivered heating oil already contaminated with water. It can be difficult to determine whether there is water in the oil by yourself because few symptoms manifest in the way the furnace works.

Skill level:


  1. 1

    Locate a valve in the oil line that shuts off oil from the tank. If the tank is above ground, there should be a valve at the start of the line leaving the tank. If yours is a below-ground tank, the valve should be near the place that the line enters your home.

  2. 2

    Locate your system's oil filter canister. The filter looks like a large jar or can. If yours is an underground oil tank, the filter will likely be located attached to or near the oil burner itself. If you have an above-ground, outdoor oil tank, the filter probably will be attached to the tank or a portion of the line near it.

  3. 3

    Unscrew the oil filter canister and examine the inside. If parts of the filter are rusty or there is a significant build-up of any rust-coloured sludge at the bottom of the filter, your oil may have damaging levels of water. Contact a professional for definite diagnosis.

  4. 4

    Examine the tank itself if yours is an above ground tank. If you notice a darkened area along the bottom of the tank, it can be corrosion caused by water sitting inside.

  5. 5

    If you suspect that your heating oil is contaminated with water, contact a heating specialist. Heating specialists use a stick coated with a special substance that changes colour in water to measure the depth of the water trapped at the bottom of an oil tank.

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