Arrived to do a performance maintenance. Set up for combustion analysis temperature split and static pressure tests. Verified operation of all mechanical and electronic components of the furnace. Checked blower for cleanliness and to see if there is any play in the bearings. Found that the fan for heating and cooling is coated in dust debris. Checked systems heat exchanger to ensure proper venting of flue gas. Performed an electronic gas leak search. Verified operation of the humidifier. Found that the humidifier panel is coated in calcium buildup and the solenoid valve is no longer flowing water. Spoke with homeowner about the system. With homeowners approval set up to return to clean the fan and install a Uv bulb in the return. With homeowners approval replaced the clogged solenoid valve and installed a new humidifier panel. Cleaned the humidifier housing as well. Tested operation of the humidifier to ensure it will not be leaking. Furnace and humidifier are operational at this time.