Performed heating maintenance on 3 year old Lennox heat pump. Cleaned return grates. Cleaned condensate drain P trap and flushed with water. Inspected blower compartment, blower wheel is clean and balanced. Noticed mildew growing on reverse side of filter, William and I discussed remedies for this including Phenomenal Aire, 2 stage UV lights and more frequent filter replacing. Temperature rise is normal. Cleaned outdoor unit and inspected electrical components. Upon departure system is operational.