Your pilot light should be cleaned when you do your yearly heater cleanup and tuneup. To properly clean a pilot light of dirt and buildup which occurs due to the products of combustion, you must use a good stiff brush. Do not use a wire brush, as it could easily damage the delicate mechanisms around the pilot light. The pilot light is the area where you will not only find the temperature bar, but also the heater itself. You must also make sure it is clean. Use compressed air to blow any unwanted dirt away from the pilot light.