Performed a 1 system heating maintenance, return filter was replaced ( unit had 4 1 inch filter stuck together,,, talked to customer about the importance of having just one filter). All safety switches were tested, flame sensor was cleaned, inducer motor capacitor was tested, monitored system’s sequence of operation to verify proper operation, checked inducer/ blower motor amp draw, inspected main drain line, return/ supply plenums were inspected, temperature differential is meeting manufacturer specifications, four no issues at this time. We recommended to install an overflow switch on the main drain line to prevent water damage in case of lines getting clogged. We also recommended to do a drain water treatment, this would remove any buildup inside the drain lines.