I just replaced the heat exchanger (complete with manifold already attached) in my Hayward H250 pool heater for my in-ground pool today. After putting it all back together and turning the heater on, there was smoke coming through the top assembly. I can not determine what it could be other than the plumbers seal grease burning off of the new exchanger.

The only other possibility would be I could have switched the two wire harnesses on the manifold when I plugged them back in, assuming that would cause it to smoke.

I am needing help on determining what the problem could be causing it to smoke. Any thoughts?