Bosch 4803 dishwasher draining problem

Hi, I have a draining problem with a Bosch SHV4803-UC12 dishwasher. Under normal operation, the basin dosen't drain.
When I disconnect the drain hose from the wall and redirect it to a bucket, it drains fine. The motor works, I can see water going through the little transparent plastic trap thing under the panel, and I can measure 120VAC getting to the motor. It *sounds* like it's working fine too, but I can't be sure.
The household-end of the drain hose goes into a pipe in the wall, not any visible above-sink air trap or anti-siphoning mechanism that I can see. It just disappears into the wall, not the garbage disposal, y-connection, etc.
When I pour water into the drain hose into the wall from above a certain level, water continues to go down, and there is little blockage. If I pour too fast, it'll back up, but it quickly clears.
If I take the drain hose and lower the end to a foot or so above the floor, water comes up, indicating there is water sitting at that level somewhere else, and I can't pour water down.
This indicates there is water above the drain somehow, and when I blow through it I'm somehow blowing this extra water through the pipes. I'm really not sure what's going on. If I stop blowing before it's clear, I can hear water sloshing in the pipe back and forth, as though something is pushing it back.
In all cases I can blow through the hose, and after *much* difficulty, can eventually clear the hose and blow air, though it's still difficult. When I then pour water in, it again backs up. We've tried drano, etc., to clear it, but I'm pretty convinced it's not a gunk blockage, since it'll take a LOT of water if I pour it in from above a certain level.
A plumber told us that this is normal and nothing is wrong with the drain in the house, and that sometimes a dishwasher needs backpressure to keep the pump primed. But I've been reading that often this is to prevent unwanted siphoning of the drain.
But I know the drain in the dishwasher can pump water into a bucket.
Is the dishwasher drain motor supposed to overpower the backpressure in the drain? In other words, is my motor somehow weak and damaged, enough to pump the water into a non-backpressure bucket, but not enough for the drain? I don't get it.
Is my drain clogged, or do I need a new motor?
thanks michael
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snipped-for-privacy@sneakemail.com writes: | Hi, I have a draining problem with a Bosch SHV4803-UC12 dishwasher. | Under normal operation, the basin dosen't drain. | | When I disconnect the drain hose from the wall and redirect it to a | bucket, it drains fine. The motor works, I can see water going through | the little transparent plastic trap thing under the panel, and I can | measure 120VAC getting to the motor. It *sounds* like it's working | fine too, but I can't be sure.
Does your Bosch use a separate drain pump motor, a positive solenoid valve to redirect the main motor, or one of those little free-floating flappers that is somehow manipulated to select between drain and circulate? I've observed that the latter seem to be very dependent on the "correct" back pressure. See:
http://groups.google.com/group/alt.home.repair/msg/7b315e0466cec0df
I suppose even a separate drain pump might now depend on the preferred (mandatory?) open-drain hookup. For what it's worth, I just installed a new KitchenAid S-series which uses a separate pump. I thought I was going to finally have to bite the bullet and make my drain configuration (which is like yours) "standard" (a non-trivial task) but it works fine. Still, the new unit is much more flimsy than the ~20 year old KitchenAid it replaced...
                Dan Lanciani                 ddl@danlan.*com
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No, this has a separate drain pump. This weekend I'm going to remove it and open it up to see if there's anything stuck in the impeller or whatever. Maybe that's sucking power away from the motor and preventing it from developing proper pressure. I'm doubtful.
Michael
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Hi,
*Sounds* more like the house drain is restricted than the d/w drain pump is bad. Run a temp hose from the d/w to a bucket/pail and run test a rince cycle to see how the d/w reacts.
jeff. Appliance Repair Aid http://www.applianceaid.com /
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Hi,
I disconnected the hose as you suggested and ran the drain cycle.
It appears the drain motor isn't strong enough to pump the water up above about the level of the main basin, or slightly above. This is far belw the ~3feet or so of the water level in the drain pipe in the wall. This suggests a bad drain pump motor assembly. However, the motor impedance reads 16.5 ohms just like it should (according to the repair guide for this particular model).
Do you think it's more likely to be a mechanical problem in 1) the motor or 2) the pump assembly? Eg impellor broken, bearings, gunk, etc. I have convinced myself it's not electrical.
thanks Michael
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Hi,
ok, found the problem. The drain impeller vanes were broken. I'll order a new assembly tomorrow.
michael
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Glad to see you are getting somewhere with it! :)

Wonder if something hard like a bone or such got in there?!?
http://www.repairclinic.com/referral.asp?R 3&N5403 Drain pump assembly SHV4803UC-12
jeff. Appliance Repair Aid http://www.applianceaid.com /
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Yeah it's weird. We've never run the dishwasher without *both* the coarse and fine filters, so I've no idea how they broke.
michael
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