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...