Descaling a Bosch Dishwasher in South Florida’s Hard Water

Why this page exists at all

Most appliances do not tell you when they need maintenance. This one does.

Bosch publishes an error code specifically for limescale building up in the heat pump. Not a generic "service required" — a code for that one condition, with its own entry in the manufacturer's own table.

An appliance maker only does that when the condition is common enough to be worth the trouble, and consequential enough that letting it run is expensive. Both are true here, and in South Florida both are truer than the manual assumes.

What scale actually does

Hard water carries dissolved calcium and magnesium. Heat it, and those minerals come out of solution and deposit on the hottest surfaces they can find — which, inside a dishwasher, are the heating surfaces in the heat pump.

A thin layer insulates. The machine puts the same energy in and less of it reaches the water, so:

• the wash runs cooler than it should, and cleaning gets worse
• the load comes out of the final rinse less hot, and drying gets worse
• the heating element works harder for the same result, for longer, every cycle

Which is why "it does not clean like it used to" and "it does not dry like it used to" arrive together on a machine in hard water. People assume two problems. It is usually one.

How often, here

The interval in a manual is written for the water the manufacturer's home market has. South Florida water is harder than that, and considerably harder in some municipalities than others.

Every three to four months is the interval we would suggest here, rather than the once or twice a year a national guide gives. If the machine shows its scale code sooner than that, believe the machine — it is measuring something and the calendar is not.

Doing it

1. Empty machine. Racks in, nothing else. A descaler diluted across twelve plates is a descaler doing half its job.
2. A dishwasher descaler, not a kettle one. Follow its own instructions for where it goes — products differ, and some are designed to be released mid-cycle by the detergent cup.
3. The hottest cycle, no eco. Scale dissolves with heat and time, and eco cycles are designed to use less of both. This is the one occasion where the long hot program is the right choice.
4. Clean the filter afterwards. Descaling loosens deposits which then land somewhere, and that somewhere is the filter in the floor of the tub.
5. Put it in the calendar. Three to four months.

The salt reservoir nobody fills

Many of these machines have a built-in water softener with a salt reservoir, usually a screw cap in the floor of the tub next to the filter.

It works well. It also needs dishwasher salt, and a great many machines here have never had any — because in the market these appliances were designed for, topping it up is as normal as adding rinse aid, and in this one almost nobody has been told it exists.

If your machine has that cap, and you have never opened it, that is worth doing today. Dishwasher salt, not table salt; the granules are a different size for a reason.

The earliest warning

Long before the code, look at the glasses.

A dull white haze that does not wash off, appearing gradually over months, is the same minerals depositing where you can see them. That is your machine telling you what is happening inside it, and it usually appears a season or two before the code does.