Our house dates back to 1955 and features several fancy items not found in contemporary dwellings. Take, for example, the Thermador in-wall heater in the front bathroom:
It has a finger-friendly design apparently intended to admit a small finger through the grille, where it can easily contact the resistance heating coil, so while we were moving in I snapped a GFI circuit breaker into that slot in the breaker panel. We advised our (very young) Larval Engineer of the hazard and had no further problem; as far as I know, that breaker never tripped and no fingers were damaged.
Back then, while adding that breaker and cleaning the first half-century of fuzz out of the thing, I evidently blobbed silicone rubber on the screw terminals of the switch:
They don’t make switches like that any more.
For reasons not relevant here, we’ll be using it for the first time since we moved in, so I spent a while cleaning / blowing / brushing another two decades of fuzz out of it.
Minus the fuzz, the heater no longer smells like a house on fire:
If that doesn’t warm your buns, nothing will!
The Smell of Molten Projects in the Morning 
Those switch contacts could benefit from gentle treatment with a diamond fingernail file or a folded piece of emery cloth.
That thing stays in place until smoke pours outta the vents! [grin]
My grandparent’s homes were full of these and all of them still worked. Additionally one home had a “portable” and outlets all over the house that were 220. I don’t recall what we did with it when they passed away but I should have kept it as a huge load bank but it was quite heavy.
If ours is any indication, those heaters had a very low duty cycle and, being built with Real Metal, should last forever.
I’m sure the “portable” version weighed more than a small child and, despite having handles, was portable in name only.
Any suggestions for a replacement switch for these Thermador heaters? We have two of them in our 1950s home and like to keep them but one does not work, I believe due to a dead switch, and the other is starting to not turn on all the time, I am suspecting the switch on that as well.
Because the switch is part of the heater, it looks like there aren’t any replaceable parts and, even if Thermador had any, I’m sure they’re long gone by now!
I’d try carefully cleaning the contacts, then look for mechanical issues. Perhaps you can use epoxy to rebuild any worn parts of the switch lever or, maybe, cut a new actuator from a sheet of non-thermoplastic material.
It’ll definitely be an interesting project, even if that’s not what you were looking for.