I installed a new heat exchanger, inducer draft motor assembly, & the back plate for the draft motor today and after getting it done I started it up and everything came on fine. The 2 shot burners where burning blue and the outlet pressure was running around 3.2 to 3.3. However, after I was gone for about 2 hours the H/O called and said that there CO monitor was going off. When I got there I started it up and the gas valve didn't want to open up but after several attempts it finally did. The flames look great but i am getting a strong smell like a rich mixture but there is no adjustments that i can see on the burners for the air. i am getting an elevated reading in the house but i took the right side panel back off to check everything and it looks sealed up with no way of sucking the exhaust back into the system. I am stumped and can't think clearly at this point. I have never had this type of issue before after installing one before. The only thing I know of right now that doesn't seem right is the rich smell I am getting out of the flue and that is it!!!. Can someone help. Could a faulty gas valve cause this to happen?