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Water accumulation inside the tank guide

Water build up can affect boilers and oil fired range cookers from producing heat. In this guide we will cover how water develops inside the tank, common problems and preventatives and how to check and remove water.

How does water develop inside the tank?

Oil tanks often collect water through condensation due to the daily temperature changes, which can cause; water build up inside the tank and microbial growth. If left untreated it will continue to accumulate; contaminating the tank, oil and heating system.

It’s important to carry out regular tank checks to spot any signs of damage. Splits and cracks in the vents and tank allows rainwater and moisture to enter, causing condensation and water build up.

Make sure your tank is topped up, low levels of oil create more space in the tank for condensation to develop quicker when temperatures change.

How does water develop inside the tank?

Associated problems with water inside the tank

Water build up and leaks

Increased risk of airborne and microbial growth

Sludge formation

Oil tank corrosion

Heating oil and aga malfunctions

Prevent water buildup inside the tank

How to prevent water build up inside the tank?

  • Service your tank by an OFTEC Registered Engineer

Read our ‘Servicing your tank guide’ for more information >

  • Regular tank inspections looking out for splits, cracks, oil spillages and leaks

  • Avoid running out of heating oil

How to check if there is water inside the tank?

You can check for water inside the tank by using water paste.

Step by step:


Apply the paste on a clean stick then insert into the oil until it reaches the bottom of the tank.


Count to around 20 seconds, then remove the stick from the tank.


If the paste changes colour this is an indication that there is water present inside the tank.


The depth of the water will be shown on the stick.


Contacting a Registered Engineer

Although you may be able to carry out the water paste test yourself, we recommend contacting a Registered Engineer who will be able to detect, report and remove water.

Find a Registered Engineer on the OFTEC website >

If you require more information on water accumulation please contact us on 01543 506117.

Contacting a Registered Engineer

How does water develop inside the tank?

Oil tanks often collect water through condensation due to the daily temperature changes, which can cause; water build up inside the tank and microbial growth. If left untreated it will continue to accumulate; contaminating the tank, oil and heating system.

It’s important to carry out regular tank checks to spot any signs of damage. Splits and cracks in the vents and tank allows rainwater and moisture to enter, causing condensation and water build up.

Make sure your tank is topped up, low levels of oil create more space in the tank for condensation to develop quicker when temperatures change.

Associated problems with water inside the tank

Water build up and leaks
Increased risk of airborne and microbial growth
Sludge formation
Oil tank corrosion
Heating oil and aga malfunctions

How to prevent water build up inside the tank?

  • Service your tank by an OFTEC Registered Engineer

Read our ‘Servicing your tank guide’ for more information >

  • Regular tank inspections looking out for splits, cracks, oil spillages and leaks

  • Avoid running out of heating oil

How to check if there is water inside the tank?

You can check for water inside the tank by using water paste.

Step by step:


Apply the paste on a clean stick then insert into the oil until it reaches the bottom of the tank.

Count to around 20 seconds, then remove the stick from the tank.


If the paste changes colour this is an indication that there is water present inside the tank.

The depth of the water will be shown on the stick.

Contacting a Registered Engineer

Although you may be able to carry out the water paste test yourself, we recommend contacting a Registered Engineer who will be able to detect, report and remove water.

Find a Registered Engineer on the OFTEC website >

If you require more information on water accumulation please contact us on 01543 506117.