Sounds to me like a textbook hot trap....I would investigate which trap is malfunctioning and get is repaired/replaced ASAP, go from the condensate return backward until you find a lower condensate line temperature. :.02:

GT

 

You have a problem. Excess water through a steam boiler will cause sediments to build up and eventually crack the boiler. I replaced a 5 year old 13 section boiler for this very reason.