linus, that is true, but both the regular and prewash nozzles are activated in this case. I'm thinking of the case where only the prewash nozzles are activated. The mechanical linkage that directs water to the appropriate nozzle(s) could have a unique position (say, the furthest position of a rotary shaft) that's entered only when the water goes just to the prewash nozzles. Theoretically it could be a concern. You would need the design details of a particular machine to know whether it's a real possibility.

In my Miele 1986, I think I remember seeing the water pouring into the Main wash and Prewash chamber during the rinses. I'll have to check again the next time I do laundry. I thought it might be doing this because the rinses take more water and so it was filling in both cups to get the water into the machine faster.

Of course my machine is 14 years old and has no linkage going on. There are three cold water valves being used to do something, so I figured one was to the main wash, one was the prewash and one was the rinse aid. These valves are all on one part that is screwed onto the cold water intake pipe inside the machine, and this is the only part that has been replaced. When the machine was open I didn't look to see where the hot water valve was ...duhhh. I think each of the valves was connected to a hose that entered the water control intake unit at different places. Now I will have to see if I can find a diagram of that part.

This is old stuff so is probably not being done anymore.

Well I found a diagram of the water control intake unit that sits overtop the detergent cups and it has 4 or 5 connection pipes in the back of it that hoses from the water valves get connected to, so no way for me to see where the water goes once it gets inside the intake control.

Frontloader dispenser mechanisms are typically of two designs.

Some have a mechanical diverter with a small motor that moves to direct the water flow into the appropriate dispenser cup.

Others have multiple solenoids that operate individually or together to direct the water flow.

I have had both that dadoes talkes about in my Mieles over the years. I was worried when I found out that Miele had changed system when I bought my w 1714 model now 9 years.

In 1998 I bought an AEG washer and dryer, both models were top of line of a new line from them just realeased. It had as stated above a mechanical diverter with a motor and a million different cogs to aid its path to the different dispenser cups. This system broke after I think 2 years of good use, only had 1 machine back then so it got use alot.

My Miele still work like a charm and only needed to replace the heater beacause of hard water build up, new to very hard water and the need to use a watersoftner powder.

My Duet has the mechanical diverter. Regardless of whether prewash is chosen or not, it'll still cycle through all four positions throughout the cycle. You can briefly catch it at 45 seconds.

https://youtu.be/8poFW-Poa88