Performed pm on oil boiler Brushed and vacuumed flue pipe and heat exchanger Replaced oil filter, nozzle, and strainer Checked all electrical connections and safeties Performed combustion and smoke tests While performing the maintenance we found very high levels of sludge at the oil filter canister. Also found some oil inside the burner by the oil pump. Cleaned up the oil and did not see any more leaking. The seal on the oil pump might be starting to go bad. Recommend reevaluating the pump next maintenance. Customer asked us to see if we could adjust the hot water temp. Upon investigation we found the balancing valve for the hot water coil was almost completely shut and was not adding much cold water to the hot line. Would recommend installing a mixing valve so water temps are more consistent. A balancing valve does not take the place of a mixing valve. Water temps were consistent around 115-120. Previous to adjusting the water temp was roughly 180*F