New Siemens Dishwasher iQ700 - curious about what a noise is

I bought a Siemens iQ 700 dishwasher recently, free standing model, and it's a very nice machine. No complaints at all. Washing flawlessly and the 'Zeolith Drying' works far better than I was expecting it to.

The blue lights are a bit sci-fi but, they're an interesting aesthetic.

I just have one technical question that someone who's perhaps a bit more familiar with these more recent BSH machines might be able to answer:

If you open the dishwasher after it's started, like say even 5 or 6 mins into the wash there's a sound which is like a fan or a vague hiss that keeps running while the door's open. It's not very loud, just like a vague sound of something blowing air. It's definitely not a fault, but I was just wondering what component / system would be making that sound?

My boss 800 does the same thing and I don't know why but I really just figured it was part of normal operation so if anyone can enlighten us with what that noise is and what it's for we'd appreciate it

I was wondering if it's something to do with the zeolite system or something.

Perhaps reading the Owner's Manual might give you a clue.

That's the Zeolite system fan.

The fan runs during drying, pulling moist, warm air in. The Zeolite basically forces the water to condense into it, releasing heat, and the air flows back into the tub as hot dry air.


Now, the mineral is damp, so it itself needs to be dried at some point, somehow.
If you'd just do it at any point, you'd get dry mineral - but you'd kind of waste the heat needed to dry the material, and then you could just as well use a heating element and fan for drying.

So, the mineral is dried during the first time any cycle calls for heat.
Instead of using the main heater, the drying fan is activated together with a heating element in the Zeolite container (that heater is about 1300-1400W in the EU).
That means you draw air from the tub, heat it, blow it through the mineral. The mineral heats up, the water stored in it evaporates and is blown out of the container into the wash tub.
There it meets the cold dishes and wash water, where the steam condenses and raises the wash temp.
That means the energy needed to dry the mineral is used to heat the wash.
That's why the fan is running, and to keep anything from overheating, the fan just keeps running for a bit, even if the cycle is paused.


On many cycles, the first fill is heated - mainly the prerinse for intensive and sensor cycles, or the main wash on other cycles.
Very few cycles don't start heating pretty quickly - for example, the Eco cycles here in the EU only heats after the prerinse stage and it's connected full or partial drain, or for example the delicate cycles don't heat in the prerinse.
Meaning that in more than 80% of cases, heating starts right after load sensing, about 4-5 minutes after the initial fill.