We have a gas heater used to heat a small home. The burner will take a while to catch once the gas is supplied, causing a loud "bang" as it ignites. It sometimes will also make a loud whooshing sound for a few seconds when it catches. We've also had the pilot go out unexpectedly once or twice. We vacuumed out the burner and it helped a little, but we still have the problem.The thermocouple has been replaced before. What else should we be doing?