I've got an LG Washer model WM8100HWA that stopped in the…

OK perfect, that means you're not getting water into the washer which is what I would suspect based on where the error occurs. That means there definitely isn't a pressure switch issue.

You need to disconnect the water supply hoses and put them in a 5 gallon bucket. Then turn the water on and make sure you're getting water out both hot and cold lines because if you have flood safe hoses they can trip and prevent water coming out. Then reconnect the hoses and try the washer again. If it still doesn't fill, you need to test all the solenoids on the hot and cold water valve for 110 volts between the 2 wires at each solenoid. You should have 110 volts to at least one solenoid. If not, return the control board and get a new one because there is no other option but the board coming bad. If you ARE getting 110 volts and water won't enter the drum, replace that valve because the valve came bad.

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So you don't get 110 volts on any connection when plugged into the valves?

OK then your control board is bad. My guess would be that you replaced the board first and you had a bad solenoid that shorted out the board, then replacing the board caused it to short out again. Either way, without a doubt you have a bad control board if you don't get 110 volts to any of the valves. You're just getting bleed voltage which is why it shows 110 volts when unplugged from the valve.

Doesn't matter, the board is bad. That was just a guess as to why it was bad, but without a doubt it's bad. We just did all the tests and it proves it's bad. It needs to be replaced.