--- title: "Scale and the Ice Machine Water Filter: Purge, Polyphosphate and a Six-Month Cartridge" description: "Where minerals settle as water freezes, what a cartridge can and cannot stop, the chlorine trade-off, reverse osmosis limits and the signs a filter is overdue." url: "https://icemachinerepair.center/guides/scale-and-the-water-filter/" date_modified: "2026-09-26" --- Maintenance and prevention # Scale and the Ice Machine Water Filter: Purge, Polyphosphate and a Six-Month Cartridge An ice machine water filter catches sediment and, with a scale-inhibiting cartridge, slows the mineral coat that forms on the evaporator and probes. It cannot remove dissolved minerals, so descaling still has to happen. Scotsman asks for cartridges to be changed after six months or when fill pressure drops, and for only the ice-making water to be filtered. By [IceMachineRepair.center technical team](https://icemachinerepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Freezing concentrates whatever the water carries, and an ice machine freezes hundreds of pounds of water a day. What stays behind forms the chalky coat on the plate and probes, and the filter and the machine's own purge are the two tools that slow it down. Read the whole guide ### What scale does Slows harvest, thins cubes, confuses probes Minerals left behind as water freezes coat every wet part. ### What a filter can do Remove sediment; inhibit scale with polyphosphate Dissolved minerals pass through ordinary filtration. ### When to change it Six months, or sooner if fill pressure drops Scotsman's rule for filters feeding its machines. ### Reverse osmosis Allowed, but not ultra-pure water Scotsman sets a floor of 10 microsiemens per centimeter. In this guide 1. Where scale forms inside an ice machine 2. What a filter can and cannot do 3. Changing the cartridge on time 4. Reverse osmosis, softeners and very pure water 5. Step by step 6. Questions ## Where scale forms inside an ice machine When water freezes on a cube plate, the ice that forms is nearly pure; the minerals stay in the water that runs back to the trough. Each cycle that trough water gets harder, and some of what it carries settles out as a pale crust on the evaporator, the distributor holes, the water pump and the probes that measure water level and ice thickness. The effects creep in slowly. Cubes release late because the crust grips them, a crusted thickness probe can hold the machine in the freeze and delay the harvest, and level probes coated in minerals need wiping to read the trough correctly. On nugget and flake machines the same crust forms inside the freezing cylinder, where it makes the auger work harder. ### The purge: water sent to the drain on purpose Cube machines drain part of the trough water every cycle to carry concentrated minerals away. Scotsman's manual calls this the water purge, notes that an effective purge lengthens the time between cleanings, and says its E series can vary the purge with the purity of the incoming water or have it set by hand. A purge set too low saves water and costs scale. ### Automatic rinse settings Many commercial machines also rinse the water system on a schedule. The Department of Energy notes that the frequency of that function can usually be adjusted to local water, and that machines are commonly found set to maximum regardless of water quality. The setting is worth checking with the manual, since every extra rinse uses water. Source: [Scotsman — Installation and User's Manual, Modular Flake and Nugget Ice Machines, Prodigy Plus A Series](https://www.scotsman-ice.com/service/User%20Manuals/17370601.pdf) — Filter only the water to the reservoir, not the water-cooled condenser; RO water at least 10 microsiemens/cm; wipe the water probe clean of mineral build-up at least twice a year; [Manitowoc — Indigo NXT Ice Machines Installation, Operation and Maintenance Manual](https://www.manitowocice.com/asset/?id=bepmjn) — Local water may require treatment to inhibit scale, filter sediment and remove chlorine taste and odor; an improperly working softener is listed as a cause of soft or cloudy ice; a dirty ice thickness probe keeps the machine from cycling into harvest ## What a filter can and cannot do Scotsman's manual draws the line clearly: suspended solids can be filtered out, but dissolved solids cannot and must be diluted or treated. A sediment cartridge protects the inlet valve and distributor from grit; it does nothing about calcium already dissolved in the water. That is why ice machine cartridges usually add a scale inhibitor. Manitowoc recommends a filtration system with a polyphosphate scale inhibitor for all of its installations and says it significantly reduces how often cleaner is needed in hard water. Local conditions may also call for carbon to remove chlorine taste and odor. - Sediment: removed by the filter, protects valves and small holes. - Chlorine taste and odor: reduced by carbon media. - Hardness minerals: slowed by a polyphosphate inhibitor, not removed. - Scale already on the plate: untouched by any filter; only descaling removes it. ### The chlorine trade-off Scotsman points out a side effect worth knowing. Most filters strip chlorine from the water, and without that chlorine the machine is more open to contamination, especially near yeast. It notes that its own filter which leaves chlorine in place improves the situation, while the freezing process removes chlorine from the ice itself, so taste is not affected. Source: [Scotsman — Installation and User's Manual, Modular Cuber Prodigy Plus E Series](https://www.scotsman-ice.com/service/User%20Manuals/17359901.pdf) — Suspended solids can be filtered, dissolved solids cannot; water purge each cycle, variable or set manually; filters that remove chlorine raise contamination risk near yeast; change cartridges after six months or on pressure drop; RO water conductivity at least 10 microsiemens/cm; water quality affects product life; [Manitowoc — Parts & Service Communicator MII-106, Ice Machine Cleaner and Sanitizer Usage](https://www.manitowocice.com/asset/?id=ojrcs) — Filtration with a polyphosphate scale inhibitor is highly recommended and significantly reduces the need for cleaner in hard water; [Manitowoc — Indigo NXT Ice Machines Installation, Operation and Maintenance Manual](https://www.manitowocice.com/asset/?id=bepmjn) — Local water may require treatment to inhibit scale, filter sediment and remove chlorine taste and odor; an improperly working softener is listed as a cause of soft or cloudy ice; a dirty ice thickness probe keeps the machine from cycling into harvest Close on a used water filter cartridge coated brown beside a new one for an ice machine. ## Changing the cartridge on time A filter works until it clogs, and then it starts starving the machine. Scotsman asks owners to check the cartridge date or the pressure gauge on the filter head and to change cartridges after six months in service, or sooner if the pressure drops too much when the machine fills. A starved fill produces short slabs and small or hollow cubes, which is easy to mistake for a failing part. Filter only the water that becomes ice. Scotsman's installation notes say to filter only the water going to the reservoir, never the condenser circuit on a water-cooled model, and to fit a new cartridge when filters are carried over from an earlier machine. Write the change date on the cartridge head where the next person will see it. - The date on the cartridge head is more than six months old. - The gauge needle falls well below its usual reading while the machine fills. - Cubes come out thinner, smaller or hollow at the center with no other change. - Grit or dark particles show up in the trough or the inlet valve screen. Source: [Scotsman — Installation and User's Manual, Modular Cuber Prodigy Plus E Series](https://www.scotsman-ice.com/service/User%20Manuals/17359901.pdf) — Suspended solids can be filtered, dissolved solids cannot; water purge each cycle, variable or set manually; filters that remove chlorine raise contamination risk near yeast; change cartridges after six months or on pressure drop; RO water conductivity at least 10 microsiemens/cm; water quality affects product life; [Scotsman — Installation and User's Manual, Modular Flake and Nugget Ice Machines, Prodigy Plus A Series](https://www.scotsman-ice.com/service/User%20Manuals/17370601.pdf) — Filter only the water to the reservoir, not the water-cooled condenser; RO water at least 10 microsiemens/cm; wipe the water probe clean of mineral build-up at least twice a year ## Reverse osmosis, softeners and very pure water Very clean water is not automatically better. Scotsman accepts reverse osmosis water on its cube and nugget machines only if conductivity stays at or above 10 microsiemens per centimeter. Ask whoever maintains the reverse osmosis system to confirm that the water feeding the ice machine meets that figure for your model. Softened water brings its own issues, and Manitowoc's troubleshooting table lists a softener that is working improperly among the causes of soft or cloudy ice. If ice quality changes after water treatment work in the building, mention it when you book, since it narrows the search. Source: [Scotsman — Installation and User's Manual, Modular Cuber Prodigy Plus E Series](https://www.scotsman-ice.com/service/User%20Manuals/17359901.pdf) — Suspended solids can be filtered, dissolved solids cannot; water purge each cycle, variable or set manually; filters that remove chlorine raise contamination risk near yeast; change cartridges after six months or on pressure drop; RO water conductivity at least 10 microsiemens/cm; water quality affects product life; [Scotsman — Installation and User's Manual, Modular Flake and Nugget Ice Machines, Prodigy Plus A Series](https://www.scotsman-ice.com/service/User%20Manuals/17370601.pdf) — Filter only the water to the reservoir, not the water-cooled condenser; RO water at least 10 microsiemens/cm; wipe the water probe clean of mineral build-up at least twice a year; [Manitowoc — Indigo NXT Ice Machines Installation, Operation and Maintenance Manual](https://www.manitowocice.com/asset/?id=bepmjn) — Local water may require treatment to inhibit scale, filter sediment and remove chlorine taste and odor; an improperly working softener is listed as a cause of soft or cloudy ice; a dirty ice thickness probe keeps the machine from cycling into harvest ## Where to stop Changing a cartridge is owner work; the lines past it are not. Do not cut into the supply line, move the filter to another circuit or adjust a pressure regulator without a plumber. If water keeps running into the machine with it switched off, or a fitting keeps dripping near an outlet, close the shutoff valve and book a visit. Written by [IceMachineRepair.center technical team](https://icemachinerepair.center/authors/technical-team/). Our ice machine technicians write these guides from their own service calls and each maker's published manuals. Sources: [Scotsman — Installation and User's Manual, Modular Cuber Prodigy Plus E Series](https://www.scotsman-ice.com/service/User%20Manuals/17359901.pdf) · [Scotsman — Installation and User's Manual, Modular Flake and Nugget Ice Machines, Prodigy Plus A Series](https://www.scotsman-ice.com/service/User%20Manuals/17370601.pdf) · [Manitowoc — Parts & Service Communicator MII-106, Ice Machine Cleaner and Sanitizer Usage](https://www.manitowocice.com/asset/?id=ojrcs) · [Manitowoc — Indigo NXT Ice Machines Installation, Operation and Maintenance Manual](https://www.manitowocice.com/asset/?id=bepmjn) · [U.S. Department of Energy, FEMP — Purchasing Energy-Efficient Water-Cooled Ice Machines](https://www.energy.gov/cmei/femp/purchasing-energy-efficient-water-cooled-ice-machines) ## Step by step. Four steps, in the order worth doing them. 01 ### Find the filter head Trace the water line back from the ice machine to the cartridge housing, usually on the wall behind or beside the unit, and note the date and gauge reading. 02 ### Stop the machine and the water Turn the ice machine off at the end of a harvest and close the shutoff valve ahead of the filter. 03 ### Swap the cartridge as its maker directs Relieve pressure, change the cartridge following the filter maker's instructions, and flush the new one to a drain for the time those instructions give. 04 ### Restore water and check for drips Open the valve slowly, check the housing and fittings for leaks, then restart the machine and watch one full fill. For the heart of your home. ## Questions owners ask. ### How often should an ice machine water filter be changed? Scotsman's guidance is every six months, or sooner if the gauge shows the pressure dropping during fills. Follow the filter maker's rating for your cartridge as well; heavy use or dirty water shortens it. ### Does a water filter mean I never have to descale? No. Filters remove sediment and a scale inhibitor slows mineral build-up, but dissolved minerals still reach the machine. Descaling remains part of the maker's schedule. ### Can hard water damage an ice machine? Over time, yes. Scale slows harvest, misleads the probes and makes pumps and augers work harder, and Scotsman notes that water quality affects the life of the product. ### Why did my cubes get smaller after a new filter went in? Check that the shutoff valve is fully open and the cartridge was flushed. A cartridge that restricts flow, or air trapped in the housing, can leave the trough short at fill time. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://icemachinerepair.center/problems/) Problem ### Ice Machine Cubes Coming Out Thin, Small or Hollow 6 causes, cheapest first Problem ### Cloudy, Soft or Wet Ice From an Ice Machine 6 causes, cheapest first Problem ### Ice Machine Making Too Little Ice for the Rush 6 causes, cheapest first Problem ### Ice Machine Water Running Nonstop to the Drain 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Ice machine water valve and filter repair The inlet valve, filter, sump float or level probe and supply line, tested and replaced when water arrives short, dirty or nonstop. ### Ice machine cleaning and sanitizing Scale off the evaporator and distribution tube, slime out of the bin, curtain and drain, with the maker's cleaner and sanitizer on its schedule. ### Ice machine harvest repair The hot gas valve, harvest assist, curtain switch and thickness probe that decide when a sheet of cubes is done and make it drop. ## More in maintenance and prevention. The routines that keep an ice machine off our schedule, from cleaning and sanitizing on the maker's schedule and changing the water filter to washing the air filter and keeping the condenser clear. [The whole section](https://icemachinerepair.center/guides/maintenance-and-prevention/) Habits that keep the bin full for years ### Cleaning and Sanitizing an Ice Machine: Descaler First, Sanitizer Second, Never Together The two chemicals and their separate jobs, the six-month and three-month schedules the makers set, how the clean cycle runs on cube, nugget and clear ice units, and the bin. Habits that keep the bin full for years ### Keeping the Condenser Clean: The Monthly Filter, the Six-Month Coil and the Air Around It What grease, flour and lint do to ice output, washing the air filter, checking the coil with a flashlight, the tools each maker allows, and the room the machine needs. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Scale and the Ice Machine Water Filter: Purge, Polyphosphate and a Six-Month Cartridge](https://icemachinerepair.center/guides/scale-and-the-water-filter/)** **[Book a visit with IceMachineRepair.center](https://icemachinerepair.center/schedule/)**