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 6.2%o2 0 ppm co 0 smoke While performing the maintenance we found high levels of sludge at the oil filter canister. After getting customer authorization we added sludge additive to the oil tank. Also saw the water heater is from 2013. Would recommend replacing it as soon as possible. Electric water heaters typically have a warranty of 8 years and recommend replacing them at least every 10 years. Noticed some corrosion and wet spots on the top of the water heater. 40 gallon electric water heater 1/2 water line