Furnace Repair near 14th Ave N. received a call from a customer who reported that their furnace was blowing cold air. I arrived at the customer's house and inspected the furnace. I found that the flame sensor was dirty and not detecting the flame, causing the furnace to shut off the burners and blow cold air. I removed the flame sensor and cleaned it with a wire brush. I then tested the furnace and confirmed that it was now heating the air correctly.