[Motorcycle Jack]

Also check the 12V supply going into the furnace with your volt meter set on AC. AC getting into a DC board is a culprit most techs will not think of. AC will kill the board quickly (your time frame about right). If you see more than couple hundred millivolts of AC your converter is bad (out near the battery compartment) and needs to be replaced. Also there are services that will rebuild your board rather than buy a new one (I hope you didn't throw them away). Send one to them to have rebuilt and hold onto it if you lose yours - you have one.