1997 Oil Furnace. Buderus G205. Was turned off for several years around 2014-2017 while property vacant.
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I had it professionally cleaned and serviced by E&V in the Fall of 2017, running at 86% efficiency (which I was told was excellent)
Furnace was used for a few months at end of 2017 and has not been refilled with oil / used since. Expansion Tank is brand new at that time- see receipt pic.