I know this is not really WOS, but thoughy I might as well post pic's of a very common HX failure I am running into.

About three years ago brought on a new customer with twenty two of these Rheem RRGG RTUs. Over the last three years I have replaced almost all except five. They all fail the same and when they fail they fail BIG.
This is the most recent unit pulled earlier this week.

Already yanked HX but the rust is a dead give away of issues...


Close up of venting side all rusted out.....


8" crack - this is found right where the Fan/Limit Probe extends in to exchanger box. About half the units I have pulled had the exact type of failure.


All the units I have pulled had the following failure.....


Posting the replacement of this unit with a new Lennox KGA RTU in the WOP forum.