Steam generators and water quality in South East Queensland

The short answer

• Scale is the main cause of steam generator breakdowns. When water boils away, its minerals stay in the tank and build up on the elements, the water-level sensor and the drain.
• Water hardness varies a lot across South East Queensland. Brisbane’s average is moderately hard by generator standards; the Gold Coast and Sunshine Coast are much softer. The water at each property should be checked.
• Harvia’s guarantee depends on its water table. The current HGX XW and HGP manuals share one table covering hardness, iron, manganese, chloride and more.
• Leave the power on. Generators drain and flush themselves after use. Switching off at the isolator stops that and invites scale.
• Descaling methods differ by brand. Harvia uses citric acid; other makers use other methods, and one forbids chemical descalers. Never borrow another brand’s method.
• Service by hours, not only by the calendar. A commercial generator can reach a home generator’s yearly hours in a few weeks.

How scale forms

A steam generator is a small electric boiler. Water comes in, the elements boil it, and the steam travels through an insulated pipe to the outlet in the room. The water leaves as pure steam; whatever was dissolved in it, mainly calcium and magnesium, stays behind.

Every refill brings in more minerals, and boiling never takes them out. So the water left in the tank becomes steadily more concentrated during a session. Once it holds more than it can keep in solution, the minerals come out as solid scale on the hottest and wettest surfaces. That is why draining and flushing matter as much as the water itself: they throw away the concentrated water before it can deposit.

Scale then causes trouble in a predictable order:

• It coats the elements, so heat transfers poorly. The elements run hotter, steam output falls, and the elements fail sooner.
• It fouls the water-level sensor. Many generators sense the water level electrically. A coated sensor misreads the level, leading to overfilling, hot water spitting from the steam outlet or fault codes.
• It flakes and blocks the drain and valves, so the automatic flush stops working and the problem accelerates.
• Concentrated water can foam, which some makers warn upsets the level sensing.

The signs are usually gradual: less steam, longer heat-up, hot water spitting from the outlet, water running to drain when it shouldn’t, or a fault code on the control. Harvia’s current generators show a service light 200 operating hours after the last service as a reminder.

How hard is the water across South East Queensland?

Seqwater publishes monthly water quality reports for each supply zone in South East Queensland. These are the twelve-month figures in the reports to August 2026, given as total hardness in milligrams per litre of calcium carbonate:

Two things stand out. First, the averages hide wide swings: water can change with the source a supply zone draws on. Second, the water authorities’ own descriptions are written for kettles and hot-water systems, where anything up to 200 mg/L is generally regarded as good quality. Steam generators are far more sensitive. One European manufacturer requires a softener above 4 German degrees of hardness, about 71 mg/L. By that measure Brisbane’s average, around 6.6 degrees, is well above the threshold, while the Gold Coast average is below it.

Because a zone average is not the water at your tap, the reliable approach is to test at the site, either with a manufacturer’s test kit or a water-treatment specialist’s analysis, and compare the result with the chosen generator’s manual. Hardness is reported in different units (mg/L as calcium carbonate, German degrees, mg/L of calcium), so ask whoever does the analysis to report it in the units the manual uses.

What Harvia asks for

Harvia’s current manuals for its HGX XW generators (2023 edition) and its HGP commercial generators carry the same water-quality table. Earlier HGX editions had a shorter table; the current one adds rows for chloride, manganese and arsenic and radon. The table lists:

The table also lists other water types that must not be used. Harvia recommends a softener on the building’s supply where the water is hard, and states that its guarantee does not apply if the water requirements are not met. Follow the table for the selected model, and ask Harvia or its Australian supplier how it applies to your local treated mains water.

How other manufacturers set their limits

Each manufacturer sets its own water rules, and they are not interchangeable:

• Softener thresholds differ. One European maker requires a softener above 4 °dH and for any public installation. Another recommends one from about 6 °dH and requires it for commercial use regardless of hardness.
• Some set a lower limit as well as an upper one. One North American manufacturer gives a recommended hardness band, with a minimum as well as a maximum, and its commercial generators also limit how pure the water can be. Their level sensors need some dissolved minerals to conduct.

So very pure water is not automatically better. Whether reverse-osmosis or demineralised water suits a particular generator is a question for its manufacturer.

Softening

A water softener exchanges the hardness minerals for sodium, so far less scale forms. It must be a type that does not cause foaming in the generator, which at least one manufacturer warns can upset the water-level sensing. Installing a softener, its backflow protection and its drainage is licensed plumbing work.

Softening does not end descaling. Manufacturers say plainly that a softener does not replace regular descaling and maintenance.

Harvia also makes a cartridge water filter for its steam generators, the HWF, whose capacity and cartridge changes depend on the water’s hardness and the volume used; see steam generator water filtration.

Draining, flushing and the isolator

Many modern generators can drain and flush the tank automatically (on Harvia generators, with the optional automatic discharge valve), and the timing tells you what each is for.

Harvia’s HGX, HGD and HGP generators with the automatic discharge valve do three things:

• After switch-off, they rinse and empty the tank. Harvia’s HGX manual says not to disconnect the power while this happens.
• Every fifth fill, they rinse the discharge pipe, so deposits don’t settle in it.
• During long sessions, an optional interval rinse (every 0.5, 1, 2, 3 or 4 hours) empties and refills the tank with fresh water. Harvia describes this for institutions where the generator runs for several hours at a time. Steam pauses for over five minutes while it happens.

Other makers wait longer: some drain an hour or more after use, once the water has cooled. Either way, the generator needs power to finish the job.

Why not switch off at the isolator? Turning the generator off at the isolator or circuit breaker after each use stops the flush and leaves the most concentrated, mineral-rich water of the day sitting in a hot tank. That is exactly the water that forms scale, and cutting power after each session is a known cause of heavy scale build-up. Switch off at the control panel and leave the supply on. How the generator is isolated for servicing is designed by the licensed electrician.

Descaling: methods differ by brand

Even with softening and flushing, some scale forms, so every generator needs descaling on its manufacturer’s schedule. The methods are not interchangeable:

One manufacturer also warns that descaler must never reach the steam pipe, because it can damage marble and limestone in the room. Never transfer a descaling method from one brand to another. For a Harvia generator, Harvia’s manual governs, including the user tasks it allows: emptying the sediment cup only after the generator has cooled for 24 hours, cleaning the water-level sensor and descaling.

Service frequency follows operating hours

Scale builds with hours of boiling, not with months. A home steam room used a few times a week may run a few hundred hours a year; a hotel steam room open all day can do that in a few weeks. That is why manufacturers tie servicing to operating hours or to the type of use:

• Harvia shows a service light 200 operating hours after the last service, and asks for a thorough service at least twice a year in community and institutional use: checking and cleaning the reservoir, the heating elements and the water-level sensor.
• One European maker asks for an extra service plan twice a year once a generator runs more than about five hours a day.
• One North American maker’s commercial range adds daily blowdown, monthly wiring and leak checks and quarterly cleaning of the level probes.

Warranty terms reflect the duty too. Harvia gives a shorter guarantee for institutional use than for a home, and it depends on the water and service instructions being followed.

Caring for the steam room itself

The room needs gentle treatment too:

• Clean with pH-neutral products. Acidic cleaners etch marble, limestone and travertine, and the Natural Stone Institute recommends a non-acidic soap-scum remover in wet areas. Use acidic products only on acid-resistant surfaces such as glazed tile, porcelain, glass and stainless steel, and never mix them with chlorinated products.
• Clean the steam outlet with mild soap and water, as Harvia advises; don’t take the outlet apart or use abrasive chemicals.
• Use only fragrances made for steam generators, and never let an essence pump run dry.
• Let the room dry and ventilate after use, as the generator and room design intend.
• Watch the seals and grout. Cracked sealant, failing grout or a door seal that has hardened lets moisture into the building. No manual we have reviewed sets an inspection interval, so a visual check as part of regular cleaning is sensible.

Commercial steam rooms

A commercial generator may run for many hours a day, so its care moves from occasional to scheduled:

Our commercial guide includes a full operator checklist, from daily checks to annual servicing, and our service page explains how to arrange servicing.