The indications on how and when to change the wick will vary, depending on the make of paraffin heater. You should therefore first read the manufacturer’s user instructions or indications on the website of the relevant manufacturer/importer. In general, heaters with wicks are more sensitive to variations in the quality of the fuel that is used. This comes about because the wick material (partly cotton, felt or fibreglass) can become blocked; the upper edge then gets hard and the wick eventually needs changing. There are no exact guidelines regarding the life of a wick ( 1 to 3 seasons is usual, providing the fuel is compliant with European directives on viscosity and sulphur, benzene and aromatic hydrocarbon content). Most notably, the ‘cheaper’ paraffin types sold at petrol stations frequently fail to comply with the aforesaid directives, and are more likely to be contaminated with harmful substances, leading to excessive wear of (components of) the heater.