Performed heating maintenance to gas, furnaces, and one heat pump. Replaced all filters. Cleared and treated condensate, drain lines and pumps. Inspected electrical connections and components. Although it is not causing any issue at the moment, I do believe I see a slight bit of change in the flame in the heat exchanger of the main level furnace with the blower comes on. This could be an early indication of a heat exchanger issue, and I just want it to be noted at this time. Otherwise units are heating normally and maintaining temperature in the home.