I replaced the two filters in my boiler's oil supply. As a result the boiler had difficulty lighting, did not always run properly and made a futting noise when it stopped.
In the past I have always used proper Crosland 489 filters. These have worked fine so long as they are regularly replaced. The replacements that did not work were the equivalent EOGB product which I bought at least a year ago. There is not much oil in the tank, but the boiler is now going properly with the old filters.