Water & Sludge Formation In Heating Oil Tanks

What Is Heating Oil Sludge?

After a long period of time, water and sludge will eventually build up in an oil tank. Sludge is a result of water condensing on the inside of the tank upon changes in temperature. As water is heavier than oil, it collects on the tank’s bottom. Water deposits represent a good place for growing various bacteria. Heating oil sludge can be a mix of bacteria, dirt and debris and tends to build up in tanks where oil has been stored for a longer period of time.

Problems It Can Cause

Sludge or water in your heating oil tank can clog pipework, damage or corrode heating systems and reduce the efficiency of the oil. Over time sludge can build up in your storage tank until eventually gets stirred up enough upon tank refilling that it then blocks the inline filters. Water may also enter the tank through any unseen cracks/rust in the body or seals of the tank. In the winter this water may freeze and this cannot be resolved until thawed.

How Do I check for sludge/water & Remove it?

To detect either water or sludge look for signs of a darkened area at the bottom of the tank, which may have been caused by erosion. We offer a Tank Health Service in which our registered OFTEC Technician will review the overall condition of the tank, check if any water is present and provide advice and tips of when you should replace it or how you can maintain your tank to extend its life.

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How To Prevent Sludge Build-Up In A Tank

To prevent sludge formation from building up we recommend using premium kerosene or a fuel additive. Bilslands Premium Kerosene can increase the efficiency of your oil and lubricate your heating oil system to reduce carbon deposits which improves the efficiency of the system and ensures complete combustion of your oil.

Other preventative measures include:

  • Heating oil tank inspection should be carried out annually by a registered OFTEC engineer

  • Ensure all lids and caps are fixed and secure.

  • Inspect outside of your tank regularly for signs of physical damage or leaks.

  • Keep any surrounding trees/bushes cut back to prevent water from leaves or branches dripping onto your tank.


If you suspect you may have sludge or water within your tank, give us a phone on 01360 660264 and one of our friendly staff will advise you.