Preventative maintenance on Lennox gas furnace. Intermittent pressure switch issue (E223) due to small amount of sediment build up on inducer port. Cleared port, pulled/cleaned flame sensor, verified proper amperage on inducer and indoor blower motor. *Homeowner changes own MERV 11 (X6670) 16x25x5 filters. Homeowner also has a power humidifier that they have turned off, and do not have an interest in using due to past drainage issues. Combustion analysis completed CO PPM 10, temp rise verified at 49 degrees in 2nd stage. System is operating properly and ready for the season. Lennox M#SL280UH090V36B-03, S#5911M09699 (MERV 11-16x25x5 customer changes own) Advised homeowner to contact Wissahickon Valley Sweep for chimney inspection and cleaning.