Navien NCB 240 Service Manual Errata?!?

[John D Wilkinson]

I've been chasing some error codes and operation issues on my Navien NCB 240. It appears as though I have half-stumbled into a solution. My six year old combi was setting an "012", and performing erratically whenever it did run. I did a by-the-book diagnostic using a .pdf service manual I downloaded from the net, and I was unable to find the problem. On one of my many rolls through the user and service parameter screens, I noticed that my unit thought it was a NCB 180, instead of a NCB 240. I then found that this could be set by the #1 bank of dip switches on the PCB, and figured my problem would solved by setting the switches as documented in the service manual. Not so. The first hint of trouble was that the given dip switch position diagram and the supporting text disagreed as to which switches were to be set. In one place it said to set switches 4 and 5, and in the next bit of text it indicated that I should set switches 5 and 6. Easy enough to work out. It took a while by trial and error to find the correct setting. The switch settings that work on my unit are not any of those the manual showed. Bottom line, it was switches 5 and 6 that set the model number, and then it was switch 5 "off", switch 6 "on", not the reverse (5 "on", 6 "off") as shown in the service manual. There is more to the story, but I'm focused on the happy ending. One further note (also not in the manual): In order to get the unit to "see" the model change set by the switches, I had to do a hard power down and up cycle. (unplug, count to 20 or so, repower). I guess it just scans those switches once on power up and sticks them in memory. Not how I'd do it, and also not what they did with switches 1, 2, 3, and 4 which override the panel and set the burn mode. Those work "right now"...

btw, The current dip switch info on Navien's site still have this wrong (or I have a unique board, not intended for the end-user world.)