The reason the light is blinking seven times is because the control board is looking for a specific temperature rise in the water in the basin and is not seeing it.
"Well, if the water temperature ain't rising, then the heater must be bad, right?"
Maybe. But other things besides a bad heater can cause the water temperature to not rise. Let's list all the possibilities here:
1. Bad heating element, which we already mentioned. Check continuity of the element. Should be something low ohms, the exact reading is not important-- you're looking to see if the element is open. If the element is open, replace it.
2. Heating element not getting voltage. This could be as simple as a loose wire on the heating element or a bad hi-limit thermostat. Or the the heater relay on the control board could be bad, in which case you would replace the control board. Trace the circuit back with your meter and the wiring diagram until you find the missing voltage.
3. No water in the basin! The control can't sense a rise in water temperature if there's no water to heat. Makes sense, right? To check this, start the dishwasher. After it finishes the pump out cycle, listen for the hissing of the water filling. If it's very quiet or silent, then there's a problem with the water fill components: bad water inlet valve or the valve isn't getting voltage. Open the door and check the fill level. Water level should be a finger width below the heating element. If it's less than this, then the water inlet valve has gookus in the inlet screen and should be replaced.
4. The pump isn't circulating water over the heating element. If water isn't circulating, you probably have a bad motor-pump assembly. You can verify by placing a glass in the upper rack and running the dishwasher (after it fills) for about a minute. If the glass is less than half full, then the pump is weak or dying and should be replaced. Honestly, this is most common cause the Clean Light blinking problem that I've seen. Here's the patented Samurai Technique® for replacing the motor-pump assembly in one of these dishwashers in less than four minutes, including beer drinking time:
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