Performed annual furnace tune-up on 3-year-old Lennox forced air system (Model GX35-30B-6F-20). Found gas valve pressure reading low at 4.6" WC, adjusted down to 1.7" WC. Tested high stage operation after 10-minute wait; attempted to adjust to manufacturer-specified 3.5" WC but valve would not respond to adjustment. Submitted parts request for replacement gas valve as unit appears to be under warranty.
