Know your product. Domestically kerosene (kero) and marked gas oil (green/agricultural diesel) are used in heating systems and cookers. Most cookers and most modern heating systems use kerosene while older heating systems tend to run on marked gas oil. The two products can easily be distinguished with kerosene being red in colour while marked gas oil is green in colour. Vat on both these products is charged at 13.5%. MGO is used in non-road vehicles most commonly amongst the agricultural community and by those involved in operating construction machinery.
Get your boiler serviced regularly.Have an idea of how much oil you have in your tank. Most tanks have a capacity of approx 1000-1300 litres so you should be able to judge how much oil you require. If you don't, have an oil monitoring system such as a watchman or use a broom handle/stick (which is clean) to dip your tank.