How to troubleshoot a Bosch dishwasher that won't finish a cycle, runs forever, or shows 2H in the display
Bosch dishwasher cycle heater control board
Water heating problems in Bosch dishwashers come down to one of two problems:
- problem with the control board not sending voltage to the heater assembly or
- problem with the heater assembly itself
How's a brutha supposed to know which is which? Ah, Grasshoppah, come with me now on a journey of Total Appliance Enlightenment ™...
Remove the front panel so you can access the control board wiring.
Put one lead of your meter in the control board where the red wire connects. That's the heater power supply line. Attach the other lead of your meter to chassis ground.
Start the dishwasher in Quick Wash.
You're looking for 120vac on your meter. Wait for it, wait for it...
If you don't get 120vac there, you're done: order the new control board based on your exact, complete model number.
If you need help opening the dishwasher door and accessing the control panel, see this video.
If you get voltage there, then you know the control board is working for the Quick Wash cycle. However, I have seen several times where the control board puts out the voltage on the Quick Wash cycle but not the Normal cycle. At this point, you need to make a current draw measurement through the red wire to see if current is actually flowing through the heater now that you're getting voltage (about 9 amps for a good heater). If you are getting current, this confirms that the heater is good; again, replace the control board. If, OTOH, you are NOT getting current flow with 120vac present on the red wire, then you need to replace the heater assembly, the specfic heater you need will depend on your exact, complete model number, which is always read from the tag on the dishwasher itself, not from the paperwork or useless User Guide.
Go ye forth and conquer!