Bosch Dishwasher Draining Problem Fixed!

Recently we acquired a used Bosh Dishwasher (a SGS6301GB/12 no less) which was supposed working fine but had 2 serious issues; firstly the door seal failed, this was pretty easy and cheap to replace, there are videos on line step through this in detail. Secondly the dishwasher seemed to finish a program too early (with the time changing to 0) and leave a load of water in the bottom, not enough to spill out onto the floor but it was clearly not right. Sometimes it would get to the end of a program but there would still be water left in the bottom. It seemed to be running the drain pump ok but for some reason it wasn't working. This is a very common problem with Bosch dishwashers if you look on the forums, not sure what exactly fixed mine but here is what I did.

1 - Check and clean filters, check for debris around drain pump impeller and damage (remove torx T20 screw in impeller cover),check for kinks and blockages in drain hose. No difference..


2 - Take off left side panel (lid slides back to remove, then take out 2 x T20 screws on front edge) and look at 'metering tank' (crazy tall transparent plastic thing that water/drain runs through). Mine had a load of unpleasant black stuff in the top left hand corner around some kind of air inlet/outlet value for the drain water. Take it out (hoses just pop off) and clean it out by sloshing hot water around inside it violently). Worked ok for a couple of days before problem returned.


3 - Remove and clean drain check valve (pull on little black rubber tab under impeller cover), at this point I noticed one of the blades on the impeller was missing. I ordered a new pump and a new check valve (it seems the rubber ones deform/swell causing drainage problems and have been replaced with a clear plastic version).


4 - Remove left side panel, remove low front panels for access to the pump (unclip/slide off the plastic kick-plate then remove metal piece that runs under the bottom of the door with a T20 screw holding it on at each side). Take out complete 'pressure chamber' assembly, dismantle completely and clean (all pops apart but needs to be done very carefully) - mine had quite a lot of fatty looking deposit in it, rather disgusting but easily rinsed out with hot water. There is a plastic pipe that runs from the pressure chamber to the front of the sump next to the drain pump, this just pulls out at both ends and mine had a lot of fatty gunk in it.The pump just twists and slides out, same deal to get the new pump back in - removing that front panel thing gives just enough access to make this possible. I also took out the control board that sits bind the switches at the top of the door (just take out all the torx screws and it comes apart). There is a rather annoying cover over the board and after some careful unclipping along 3 sides to remove it the main board can pop out. Mine looked like it had some dodgy joints on the pins of the relays and around the small transformer and diodes - I'm not an expert on this but look for a faint band around the circumference of the solder joint. I re-flowed the joins with a bit of extra solder then cleaned up around the soldering and all the edges where the connectors slide on. This all took a couple of hours but it worked! Now draining perfectly and just leaving a very small amount of water at the bottom of the filters like dishwashers do.


5 - Fit shiny new plastic drain check valve when it finally turns up...


By step 4 I was pretty determined to fix the thing and it's hard to pinpoint what the problem was exactly. I'd be surprised if the impeller blade caused the issue or the control board, I think it more likely to be caused by the fatty gunk in the pressure chamber and associated hose (a lot of the info I found on forums supports this). Although, if you're going to the bother of taking it all apart it's probably worth sticking in a new pump as they're pretty cheap from ebay. Hope this info helps someone out there! Below are the pics I took for reference when I was doing it, of control board, pressure chamber, metering tank, and pump.