Siemens SN25314 Dishwasher not filling

[FortyForty]

I have a 10 year old Siemens dishwasher which is in excellent condition except that the normal flow of water through the water inlet unit sometimes fails and now routinely fails. At the correct points in the cycle the water inlet valve opens and water enters the water inlet unit. This is a plastic unit that is the height and depth of the dishwasher and has several compartments connected by built in capiliary tubes.
What should happen is that the water fills the top compartment to the height when the capiliary tube connecting it to the main compartment is filled and the water then starts flowing through into the main compartment until it also reaches the height of the top of its draining capiliary tube at which point the water should flow down the tube and by capiliary action continue to flow until it empties the whole main compartment into the base of the dishwasher. This should repeat 3 times to fill the dishwasher to the required level.
What actually happens more often than not is that the top compartment fills, the main compartment starts filling but does not reliably reach the top of the draining capiliary tube and instead the water continues to rise up the top compartment instead until it overflows into a safety outlet into the dishwasher itself.
My initial thought was to buy a replacement water inlet unit but on visual inspection I can not see any fault with the old one and I suspect that the issue may be elsewhere. My next thought was that it could perhaps be an issue with the Water Softener Unit which is tightly coupled to the water inlet unit. Indeed this seems the most likely culpret but it is also an expensive item to replace and find I have got it wrong.
Any advice please - particularly any tests I could perform to further identify the part at fault. I can confirm that all the solenoids and motors are working and water is flowing just not through the correct path. Pressures in the tubes or chambers are not right such that water ends up filling the top chamber before the main chamber overflows.

 

[assuhors]

The usual reason for this, is that the inlet solenoid valve is not letting the water in fast enough.I imagine on that model you have the grey box under the sink.You can check the filter on the inlet solenoid,disconnect it and make sure you have good water pressure.

 

[FortyForty]

Thank you for your reply although I don't believe the inlet valve is causing the problem. Water always flows OK into the top chamber which is vented and so not under significant pressure. The water then flows out of the top chamber once the water height reaches the top bend in the capiliary tube that goes down to the Water softener inlet. The pressure on this is caused only by the height of the water in the top chamber and not the rate of flow of the water on the inlet. When the system fails the top chamber overfills so the pressure will then be at its highest.
The water softener is in the path between to top and main chamber and so could cause the flow rate into the main chamber to be reduced. I have also noted that the smaller 4th pipe off the top of the water softner that goes up to the top of the dishwasher and drips out into the condensation pit fills and starts leaking water out.
Does all of this further confirm the issue is with the water softener restricting flow?

 

[FortyForty]

Many thanks to assuhors you were right. I tried bypassing the water softener and the problem persisted so i took courage and ordered a replacement inlet valve. What I had not realised was just how fast the water inlet should be. It used to take 5 times or more as long to fill as it does now. So thanks again!

 

[Bordeaux]

Hi FortyForty,
I have the exact same problem as you describe in your first paragraph. However, this problem arose after I replaced the water inlet valve (which I thought was causing my original problem of water not going into the system).

It is certainly the case that water is getting into parts of the plastic tank you describe (though my machine's beko), but as you describe fills up too much and overflows before letting the water into the body of the machine.

I did manage to do a cycle by regulating this: Basically, turned the machine off when the level rose to high, then on again, then off again etc until the machine had sufficient water in the basin and clicked onto the next stage of spraying/washing etc.

I don't know if this helps, but wanted to share, and will update if I find anything knew (maybe i need to check the tubes, between the plastic tank and basin in the machine?).

Good luck