Because my oil company predicted only a 15% increase in efficiency I passed on the $6000 replacement estimate I received last year. We burn approximately 1100 gallons of oil a year for steam heat and hot water. The issue now is that it seems the hot water coil is leaking as the boiler keeps overfilling. The tech replaced the feed valve hoping that would solve the problem but it did not. The boiler is 70 years old and not otherwise leaking, I'm told that the cast iron will last forever! The hot water coil cannot be replaced. My options are to replace the entire unit or install a separate hot water heater. Looking for some opinions.