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CvW

Bosch SHV99A13UC19 Dishwasher Check Water Supply

6 posts in this topic

Hi everyone and I hope you are well.

 

8 years ago, we bought a SHV series dishwasher that has served us well all these years. The dishes come out clean, and maintenance has been pretty minimal (monthly gunk cleanings from the filter). Up to now, our only equipment failure on the dishwasher was a broken rinse aid dispenser that suddenly became way more enthusiastic about dispensing rinse aid. Once that part was replaced (pretty hazardous metal sharpness around the dispenser, I might add) everything went back to normal... until this week. 

 

Earlier this week, the LCD on the unit reported "check water supply". This seemed like an odd message given that the water supply here is filtered down to 25 microns and no one had messed with the valve controlling the hot water supply. But I dutifully undid the baseboards, accessed the valve (thank you Bosch for making it easily accessible) and tested the coil. That came out as "OL" on my fluke, making me think that the solenoid was bad, so I ordered a replacement from Repairclinic.com.

 

Installed the new valve and then also tested the old one. Both showed continuity (ARGH) and hence the issue was not with the valve. I checked around the dishwasher, with my borescope, the base pan has zero water in it and if I jiggle the red plunger on the right side of the dishwasher, the pump dutifully comes on and sucks the sump dry. 

 

Based on the wiring diagram, I now suspect a bad main board. The wiring diagram drawing enclosed with the washer suggests that one leg of the solenoid valve should always be hot, while a Triac controls the on/off action to Neutral on the other leg. The 120V supply also goes through the float switch, which disconnects the water valve from line power in case of a leak and the parallel resistor sensor / input as well. 

 

I even started a cycle where I manually added water to the sump and the machine ran it just fine (took several fillings as the drain pump did its work). So at least now the dishwasher is no longer accumulating delicious anaerobic food scrap smells. During the cycle, the unit heated the water just fine and the dishwasher came out very clean. Given that the valve is OK, there is no water in the base of the unit, the float switch works as intended, the heater, the drain pump, etc. and the washer can complete a cycle if water is added manually, I wonder which component you think may be at fault here. 

 

I currently suspect its either the water switch (m5) being stuck or that the main PCB is somehow defective (i.e. solder joint or component failure). Do you think I am on the right path and how would you test to confirm? Ideally without having to pull the washer from the cavity...

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Need appliance parts? Call 877-803-7957 now!

When the D/W is calling for water:

 

... is there 120v across the Water Valve ?

YES, bad Valve

OR

... is there 120v on one side (... or on both sides) of the Water Valve (with respect to ground / neutral)

If so. if you connect the other side (Controller Triac side) of the Water Valve to ground / neutral,

the Water Valve should then "work"

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Thank you and will check tonight. The last time I measured no potential across the valve. However, I did not check potential relative to GND.

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Your model also uses the pressure style switch w/diaphragm in the water inlet assembly located on the left side of the dishwasher.  Might just need a good cleaning but you will have to remove the unit to access.

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Ok, back to report on my progress. The good news is that the dishwasher is once again washing dishes. The bad news is that it took two visits from our local service technician to do it. So I got to wash a lot of dishes. Oh well.

 

Long story short, the most likely initial culprit was the pressure switch / float assembly on the left of the washer being gunked shut. A nice black layer of mold / grease / etc. had made the red float stick, the bottom of the diaphragm switch was also somewhat coated (but not blocked). That assembly was easily cleaned, I will keep the original (now cleaned) part for future repairs. 

 

In the course of measuring the voltages on the water valve, I caused an accidental short, with somewhat predictable (though for me spectacular) results. It's one way to wake up. I knew that the logic board was likely borked and when the washer still would not run despite the (relatively inexpensive) switch assembly being swapped out, the technician ordered a new one. Today, it got installed. 

 

In the process, we also cleaned out the inlet valve, which had gotten pretty solidly gunked up too in places. This is where I wistfully remembered all the fine brushes from my riflery days. They would have been so useful cleaning out that inner chamber with the check valve. Instead, I relied on a bent coat hanger, lots of water, and lots of shaking, soaking, swearing, etc. to get the chambers reasonably clean. When the motor drive board came out, I was actually somewhat happy that this episode required its removal.

 

The board showed the apparently common issues relating to the heater relay pins showing serious solder deterioration (see red arrows in image below). Based on this and other people's anecdotal experience, it's likely a good thing to look at these periodically (just like the check valve) if your Bosch dishwasher is 8 years old like ours and gets used regularly. I found it somewhat hilarious that the connector got two beefy pins for interfacing with the PCB trace, while the relay only got one (perhaps undersized?) pin. I also found the discoloration of the solder mask above the high-power traces to be of interest as well.

 

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But why stop at discoloring soldermask when you can actually make it leap off the board? That's what I managed to do when I accidentally shorted the water valve to GND. The copper traces blew off the solder mask and warped from the brief, but intense heating. Brilliant. I guess a board repair is out of the question now...

 

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On the topside, it is apparent that what was indicated as a triac controlling the water valve is likely 3A relay instead, at least on this revision of the board. Also interesting was the use a switch-mode power supply to make 9VDC for the relays and the use of linear regulators for other voltages. Plenty of unused positions on the board indicate that there are other versions of the board that require far more solid state components. Perhaps that's reserved for the space station edition? 

 

Anyhow, and most importantly, thank you all again for the help. I really appreciated it. 

Edited by CvW

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One more question... is there any way to prevent chunky and greasy gunk from  accumulating in the check valve, pressure chamber, and elsewhere in the washer? For example, should we be running the sanitization cycle once a month to help wash that stuff out? If so, are there any kinds of detergents, etc. that you can recommend to help the washer rid itself of this sort of gunk?

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