The website DoItYourself.com recommends using a vacuum cleaner and wire cleaning brushes to clean a gas boiler. It is also necessary to have a set of screw drivers on hand to remove the vent stack and boiler cover.
A digital camera is an additional optional tool to use when cleaning a gas boiler. While disassembling the boiler, take photos of every step so it is easier to reassemble the pieces after cleaning. It may also be a good idea to have the users manual for the boiler on hand prior to cleaning. The manual shows how to turn the boiler off prior to disassembly and turn it back on after cleaning is complete.