Limescale and water hardness in combi ovens: why it matters and what to do
In a combi oven, the parts that make steam are in constant contact with water. Calcium and magnesium dissolved in the water come out as limescale as it heats up. Scale reduces steam output, strains the heating elements and misleads the sensors. Knowing your water hardness is the first step to setting the right maintenance interval.
- Limescale forms when the calcium and magnesium in hard water come out of solution as it heats.
- Symptoms: slow or weak steam, longer cooking times, steam and water error codes.
- Measure your water hardness first; the maintenance interval and the choice of filter depend on it.
- Fully treated water is not suitable for every unit; the permitted values are in the manual.
How does limescale form?
Mains water contains dissolved calcium and magnesium. When the water is heated, and especially when it evaporates, these minerals stick to surfaces as solid scale (mostly calcium carbonate).
Because the combi oven’s steam generator evaporates water continuously, scale builds up most there: the water leaves as steam and the minerals stay behind. In boilerless (direct injection) ovens, scale can also build up in the water nozzles and around the fan.
Which faults does limescale cause?
- Steam output falling or stopping.
- Level sensors measuring incorrectly and water error codes.
- An insulating layer forming on the heating element, leading to overheating and burnout.
- Blockages in the water inlet valve and nozzles.
- Longer heat-up and cooking times, higher energy use.
Scale does not conduct heat well. The heating element has to get hotter to heat the same water, which means both wasted energy and a shorter element life.
Is the water hard in Antalya?
Limestone (karst) terrain is widespread in and around Antalya; a large part of the city sits on travertine layers laid down over centuries by lime-rich spring water. In many areas the mains water is calcareous.
Even so, hardness can vary by neighbourhood, source and season, and the values are different again in Burdur and Isparta. So base your decision on a measurement of your own water rather than on general belief. You can get your area’s water hardness from the water utility (ASAT in Antalya) or measure it in the kitchen with a test strip.
How is water hardness measured and read?
The most practical way is total hardness test strips or drop tests; water treatment companies also carry out measurements. Hardness is given in different units, so check the unit when comparing:
- 1 French degree of hardness (°fH) = 10 mg/L calcium carbonate (CaCO₃)
- 1 German degree of hardness (°dH) ≈ 17.8 mg/L CaCO₃
- 1 °dH ≈ 1.78 °fH
The permitted hardness value for your unit is in its operating and installation manual. Convert your measurement to the same unit and compare it with the value in the manual.
Filter, softener or treatment?
- Ion-exchange softeners (regenerated with salt) hold back calcium and magnesium and noticeably reduce scale formation. They must not be left without salt.
- Cartridge water filters made for the unit reduce hardness and trap sediment. Their capacity runs out depending on the water hardness and the amount of water used; the replacement interval is set accordingly.
- Reverse osmosis (RO) and fully treated water is very soft and can be corrosive to metal surfaces. Many manufacturers specify a minimum hardness and a chloride limit; check the manual before using it.
The right solution depends on the type of unit, the water hardness and daily water consumption. Follow the manufacturer’s water quality instructions when choosing.
How often should descaling be done?
There is no single correct interval. Three things decide it: the water hardness, how much the oven works with steam, and whether a water filter or softener is used.
On ovens with an automatic descaling programme, run it at the interval the manufacturer recommends and use only the recommended product. On ovens without such a programme, descaling the steam generator is part of scheduled maintenance.
Looking at how much scale has built up in the steam generator at the first service is the most reliable way to set the right interval for your own kitchen.
What can you do yourself?
- Measure the hardness of the water supplying the oven and note it down.
- If there is a filter or softener, check its indicator and salt regularly.
- Choose descalers and cleaning products only of the type the manufacturer recommends; unsuitable acids can damage gaskets and metal parts.
- Do not put off maintenance once you notice steam production slowing down.
Are dishwashers and ice machines affected too?
Yes. In a dishwasher, scale builds up on the heating elements and boiler, narrows the rinse nozzles and leaves white spots on glasses. In an ice machine, it coats the evaporator and water distributor, making the ice smaller and cloudy. For units on the same water line, one hardness measurement serves them all.
This guide contains general information; the values in your unit’s manual and the manufacturer’s instructions take priority. Leave work on electrical, gas and refrigerant circuits to a technical service.