I have a 17 year old Lennox whisper heat Furnace with a delayed ignition. There are three burners. When cold started, the pilot light will ignite, then the middle and left burner will ignite. The flame sensor and pilot is on the middle burner. The right burner will take an extra few seconds to light, usually resulting in a build-up of gas and a soft to loud whoosh bang. This only happens on a cold start. If turned off and back on ignition is fine. The gas pressure does not seem to change this. All the the burners have been removed and cleaned. The left and right burners have been swapped and same result. The only issue I can find is a weld for the wing on the middle burner possibly not letting the wing carry a flame to the right burner. Could this be the issue. Doesn't make sense because this is a factory weld is as old as the furnace. Can't believe no one has noticed this during a service call. Please help. Whoosh bang gets very loud sometimes and don't want to have an explosion.
