Scalemaster^® i-Mag^® System Filters can be supplied as a single unit or as part of a Part L Compliance Pack. They are available in both Hard Water and Soft Water Packs and include the items you will need for Part L Compliance, System Filter, Chemical Inhibitor, Cleaner and a 15mm Electrolytic Scale Inhibitor (in the Hard Water Pack). Scalemaster^® i-Mag^® system filters are fitted close to the boiler in order to keep the heating system clean long term. Heating water is always sent from the boiler around the radiators and back to the boiler again. The i-Mag^® system filter is fitted on the pipe that returns water back to the boiler.  As water passes through the device, a large magnet attracts any rust out of the water onto the magnet so that only clean water is passed back to the boiler. The system filter will need to be cleaned out once a year or so. Commonly installed as part of a new boiler installation. NOTE: For a heavily blocked system a magnetic filter alone may not be enough to clean it, you may need to power flush the system first.