Norcold 1200lrim Cools in back up

A defective Thermister will still OHM (test) correctly. Are you positive you replaced with the correct Thermister? There are 2 Thermisters for the 1200 series. Make sure you get the one for your Model/Serial number. Thermisters rarely fail. I would try one more thermistor and if the refer fails again then replace the Control board. What work has been done on the refer? Have you had the rear fans and fan tstat ever replaced? IF the fans are more than 4 years old, I would replace them and the fan tstat and run a jumper bypass from the fan tstat at this point. IF the fan tstat and/or the fans are not operating WHEN they should THAT will cause a NO CO. I have rarely had a thermistor cause a NO CO trip. Doug

I would say Camper Paul has it.. If it works in bypass. but not in automatic, and you have already replaced the thermistor twice.. Not much else left.

Check with dinosaur boards (Delete space add www. and .com) and see if they have one for it. If they do I will tell you what I found when I ordered one from American RV in California.

Mine is for an Atwood furnace.

First thing I notice out of the box was a general feeling of QUALITY, Nice big heavy traces, every solder joint looked pristine (And yes, I have the credentials to make that judgement), the board looked to be very well made.

Upon closer inspection (I have some engineering training however I never completed the degree) I found even the design was superior to the OEM board.

Made in the USA as well.

I highly recommend them.

Oh,, As for the furnace.. Since I slipped that board in it has failed one time.... I ran out of propane.

Possible defective control board.