This is what Error Code 170 says: "Possible Front board service condition or unit not correctly wired to 120 VAC. Contact an authorized service representative" I had no way to test the board other than to check the connections so I called out my Local Service Rep. He swapped out front board and back board but no change. Swapped out flow sensor and problem solved (original front and back boards re-installed). $395 for part and labor.
FYI; I have the old style salt cell and flow sensor that are in two separate locations in piping. The new style salt cell that has the integral flow sensor port is having flow sensor problems. So, when I have to replace my cell, I will leave the old style flow sensor in it's location and put a plug in the new cell's flow sensor port.
Also: when this problem first started, my PDA started showing a salinity level of 25,500 instead of the normal 3000 to 3500 range. I found out that that was due to the flow sensor failure. At the time, I could not find any information as to why the 25,500 reading was coming up. Maybe if I had found this site back then, I could have saved a lot of time and frustration.