Has anyone experienced their seat heater making the seat very uncomfortably hot? My 2013 GLK350 driver's side seat back heater makes the lower left side (only that area) of the seat so hot it's hard to keep your hand over it. Was not noticing it due to wearing a heavy coat, but put my hand there to reach into the door pocket and got a helluva surprise. It's so hot, I'm concerned the seat surface will melt.

The timer works just like the passenger side does (passenger side doesn't get hot like this).

Any ideas how to open the seat back for a visual inspection? Currently I'm manually shutting off the heater.

Many thanks

 

Hot spots in these seats (not confined to Mercedes) is usually caused by the heating element developing a high resistance spot from continued flexing. They usually fail a short time after this is noticed, sometimes with a bit of burned smell. The only remedy I know is to replace the heating element.

 

Not sure about that... higher resistance would reduce current flow and that would result in less heating.

 

True, but when that happens, the high resistance spot gets almost all the voltage drop and the heating is concentrated in a very small area.

If there was an internal short in the heating element that would cause the bypassed section to go cold, and the remainder to overheat. I think the design would make that unlikely, but anything is possible. Similar technology to a heating blanket.

I’ve never replace a MB seat heater, but many in domestic brands. When I pulled them out, there was always a burned spot on the pad and the iron ribbon element was open at that spot.

 

Arc lighting is a good example of the kind of "hot spot" that an "almost open" in a circuit can create. FWIW, I recently had an open heating element in my oven (a hidden, below-the-floor of the oven element). Where the open occurred showed clear signs of a LOT of heat being generated. Maybe not as much as the entire element does at full song, but clearly it got MUCH hotter than the rest of the element ever did.

On a related note, this kind of failure will never blow a fuse, since the total current is less than normal "max", unless somehow the open circuit moves and finds a nearby ground to play with...