I checked it as far as the heating element in the seat is open circuit and has to be replaced under extended warranty ($100). Problem is that I take my truck out of town to have work done on because I refuse to let my local Ford dealer make any more money off me. It started to get cold here, so I might have to go to a Dodge dealer LOL. Good thing is the wife won't take my truck anymore.
I just replaced the drivers side heating pad on mine last month. So hopefully this will help out a bit and I can write this in a way everyone can understand it.
Easiest way to check it is to do a continuity check on the heat pad wiring. Check the reistance, if it is infinite ( open circuit) you will have to replace the heating pad. If you are having trouble finding the connectors and checking it just pull the seat out that will make it easy. Chances are you will be pulling it out anyways. The heating element in the backrest rarely fails but the one in the cushion is very common.
To replace the heating pad element you will need some new hog rings and a pair of hog ring pliers. Once seat is removed pull the switches and plastic trim off the side. Unbolt metal seat bracket that holds the power seat motor from the metarl seat frame. Now you can remove the pivot bolt from the left side of the seat and push the seat to the right and off the pivot pin. Fish all your wiring out of the way and your control cable for you backrest adjustment knob. Now you can seperate the upper part of the seat from the lower. You can now remove the seat cover, be careful not to pull too hard on the cover to expose the hog rings or you will pull the metal rods out of the seat cusion foam and that will ruin it, the cover will no longer stay tight to the seat foam. If I remember correctly, there are 4 hog rings down each side of the cushion and 3 in the front section and 2 in the rear section.
It is easiest to cut all the old hog rings in half to get them apart, pull the seat cover off, replace the heating pad, then reinstall the seat cover securing it in place with new hog rings. Reassemble your seat cushion to frame and upper seat section, reinstall wiring and power seat frame, then reinstall. I marked where the wiring went with a sharpie to make it easier to remember where it all went.
Shouldn't need a part number for the hog rings, I believe they are all the same. A lot of parts stores should have them, or maybe someone like harbour freight or another tool supplier. Here in B.C we have a tool and equipment supplier called KMS tools and you can buy the pliers and hog rings from them. Any upholstery shop should have them, they have been used for years and years on seats.
Today the dealer replaced the bottom element. It took about 3 hours and I paid $113.00 which is my deducible. They said that Ford pays $130 for the element, if I was out of warranty, I most likely be looking at over $300.00.
My driver seat heater stopped working in my 2018 f350. Took it to the dealer. They said blend door element. I knew that was wrong. Of course heater still not working. I guess this has been an ongoing thing with ford.