My 12 year old furnace developed a carbon monoxide leak. Fortunately - we have a detector. I was told it was Inducer assembly and it was replaced. I was also told problem had to do with venting pipe. It was 3 inch; pipe that went down to 2 inch; pipe at the house wall. He said back pressure caused part to fail and changed the pipe to all 2 inch; (but chart says at my altitude I should have 2 1/2 - 3inch; pipe!). Three months later furnace failed again - this time could hear water when it came on! The condensate pump was packed full of mud! how does this happen when it was just repaired 3 months previous (or did service man not bother to check entire furnace???) Then - three months later another problem. The circuit board fried - we smelled electrical type burning and next morning realized furnace was not working again. Had to replace the circuit board! What is going on here? Should a furnace fail after only 12 years to this degree? Never had any problems until now.