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SubZero_Wolf Expert
SubZero_Wolf Expert, Home Appliance Technician
Category: Appliance
Satisfied Customers: 340
Experience:  Licensed Appliance Journeyman
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My Bosch dishwasher runs though normal cycle by circulating

Resolved Question:

My Bosch dishwasher runs though normal cycle by circulating pump does not come on. I have established that there is no power to the pump. I replaced the control board with no effect therefore it appears that the replacement control board is defective of there is some other trigger that the control board is missing. Drain, fill and heat are working. Is there are trigger I'm missing.
Submitted: 11 months ago.
Category: Appliance
Expert:  SubZero_Wolf Expert replied 11 months ago.

SubZero_Wolf Expert :

Hello, I can help you with this. There is a chamber on the left hand side (opposite pump) that has a switch on the top. When water fills the unit it engages the switch to send power to the circ pump. I would remove the side panel and check out that pressure switch. There are two switches, one is above a red stick. That is the flood switch. Its the other switch mounted on the pressure chamber you want to check. Let me know, Thanks, Sam

Customer:

Thanks. I

SubZero_Wolf Expert :

No problem. Just let me know what you find or if you have any other questions. More than happy to help. Thanks, Sam

Customer:

Sam. I haven't disassembled the dishwasher yet but I checked the schematic and couldn't find any reference to a second switch - I wanted to check the switch condition from its input to the controller board. The schematic shows the float switch (Safety, which turns the drain motor on when activated), a flow switch (in series with the heater and thermostat), an aqua sensor and a reed switch (rinse aid sensor). I checked the Repair Clinic video showing how to replace the float switch and I saw the red stick you mentioned but only 1 switch - the float switch. I checked the Repair clinic parts list for my model (Bosch SHX46B02UC/21) and only found one switch - the float switch (Safety). Does my model have a second switch and, if so, is this connected to the controller board? My machine drains, fills and runs through it's cycles correctly including heating the water but no circulating pump. Thanks. George.

Customer:

Hello Sam

SubZero_Wolf Expert :

Hello, I have been looking up some more info on this specific unit. Also have been having issue with our site.

SubZero_Wolf Expert :

This is a machine that is between two models on the inside.

SubZero_Wolf Expert :

They have the pressure chamber but tech sheet says this unit has switched from pressure fill to timed fill. That's why you have the chamber but no switch.

Customer:

No problem. I have to leave for a few hours so can't chat. Please let me know what you discover. Talk to you later. George.

SubZero_Wolf Expert :

When you replace the board which did you do? upper or lower

SubZero_Wolf Expert :

Will do.

SubZero_Wolf Expert :

I'll just fill you in here and you let me know when you get a chance to check stuff.

SubZero_Wolf Expert :

Most Boschs only have one board, this unit has two. The power from the lower board to pump wire is only a foot long, so that should be easy to check. Our circuit for this pump then is Upper board sends low voltage to lower board telling it to opperate pump. Lower board send voltage to the pump back to nuetral. Let me know what board you replaced. Thanks

Customer:

Sorry Sam but I have only 1 board. I pulled the 4 wires from the motor and capacitor, pulled the controller board motor connector and buzzed each lead - the motor wires go directly from the motor to the controller board per my schematic. There is no other circuit. From your research it looks like I have a timed fill. So when that time is up does the controller operate the circulation pump with or without any further input? If there is another input I need to know what it is so I can check it. If there is no further input my then new controller board probably has an issue and I should try a new new one. If you need anything from me to aid your deliberations such as the schematic please let me know. Thank you. George.

SubZero_Wolf Expert :

Thanks George. You only have one unified board that is up in the control panel area? You do not have a lower board near the circulation pump? Thanks for the offer of schematics but I have access to all information on this unit, however they made this machine right as they were retooling the factory for the new line they make now. Regardless of boards you are correct that I have verified that this is a timed fill unit. Since they have removed the pressure chamber sensor they only thing that controls when the pump turns is the board(s). If you only have the one upper board then that is suspect. I know you verified that there was no voltage to the pump. Have you verified that the pump is not shorted out and that is what killed the board. Sorry that this has been a pain. You have an odd Bosch and an unusual issue, We can get this working though.

SubZero_Wolf Expert :

Just to be clear about the retooling thing, when I look up this model, there are multiple parts diagram show without serial breaks. Service manual show all version not what you have specifically. Even bosch isn't sure

Customer:

I do not have a lower board near the circulation pump that I can see but in any case the pump wires go directly to the controller and so there is no other circuit. I have compared the impedances between all pump and capacitor terminals with the new pump I got from Repair Clinic that I have not attempted to install and measurements are the same within an ohm or two. I will get another controller board and see what that does. Keep your fingers crossed. I will be in touch. Thanks for your assistance. George.

SubZero_Wolf Expert :

Thanks, XXXXX XXXXX we eliminated that. No short in the pump. No pressure switch, the unit is on timed fill. No secondary board. One other thought. A few factory boards come with jumpers that plug into them for the intermediate models, to program specific functions. This would have to be moved to the new board Do you have the original board? Did you notice anything like that?Thanks

Customer:

In my buzzing out yesterday I found that the schematic is not completely correct - the door switch contacts are between the circulation pump and the controller board (12.3.1) not directly to power neutral as shown on the schematic. (The schematic shows the drain pump connected to the controller board at 12.3.1). There also appears to be a third quite large motor in the back behind the circulation pump. I have no idea what that is. Further investigation into this however may not be necessary since I then checked the old board as you suggested found no jumpers but did find evidence of over heating, opened it up and found that the heater relay (K1) had over heated, cooked and burnt away part of the track thus removing power from at least relay K3 and perhaps K2 as well. The circulating pump relay K4 does not appear to be directly affected and looks to be in good condition. The problem, therefore, could be as simple as a defective heater relay. I will attempt to remove that relay, jumper the track and see if the machine works without the heater. I will also check to make sure that the heater circuit is not a short. I'll let you know how I get on. George.

SubZero_Wolf Expert :

George. The only thing that is behind the circulation pump (per diagram) is the heater and flow aensor and the diverter for the spray (top/bottom)

SubZero_Wolf Expert :

The Relay on the heater circuit is very common (I soldered mine at my house yesterday). Don't even worry about replacing the relay I'm sure it the soldier. Just glob some on and that should be ok. If you jumpered that cuircuit without a load that would be bad. An open heater relay will not affect the circulation pump curcuit. Also if the door switch was bad you wouldn't get any fill or drain. I would replace the original board with some solder on the heater relay.

Customer:

Thanks. What's the best way to remove the protection from the track so I can thicken it up?

SubZero_Wolf Expert :

Honestly I don't know how those boards are printed so I don't know the proper etching solution.I have never had to remove any of the tracking. I have just cleaned up the relay joint itself.

Customer:

I removed and checked the relay and it is OK. I soldered a small wire to the joints, put it all back together and the machine is running as we speak. It appears to be fully functional but we'll see if it completes its cycle and I'll let you know. Thanks again for your assist.

SubZero_Wolf Expert :

Glad to help. It's very stange that you had no voltage to the pump with an open heater circuit. That is not supposed to be possible. Looking forward to hearing the good news.

Customer:

Sam. The reason the heater relay issue affected other circuits is that the heat actually cut the track to the other circuits as stated in my 11/3 note at 0613 hours. It appears that the cross sectional area of the track at the heater relay contact joints is insufficient for the power being drawn by the heater. If I have any further trouble with this I will replace that section of the track with wire able to carry the load. The machine has completed its test cycle and one real washing cycle overnight. I think we can now close this support session. Thanks again for your excellent advice which I will reflect in the rating. Keep up the good work. George.

SubZero_Wolf Expert, Home Appliance Technician
Category: Appliance
Satisfied Customers: 340
Experience: Licensed Appliance Journeyman
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