I have a Tanis heater in my plane and it’s impossible to push the plug completely into an extension cord. I’ve been struggling with this for years. I called Tanis today and found out that until about 12 years ago their plugs were larger to fit old style extension cords which apparently are larger than modern ones. So if your Tanis heater is more than 12 years old you probably have the old style plug. For $25.00 they will sell you a new plug that works with new extension cords. https://www.tanisaircraft.com/tp02770-115.html
