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Gaggenau Oven

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Sep 25, 2011
Garbsen, Germany
Yes, this is off-topic for this forum, it's the wrong kind of machine, but bear with me. (If the moderator Charles feels obliged to delete this, it's OK, I won't sulk.)

A few weeks ago, the convection heat in our oven failed. Not a surprise: my wife likes to bake bread and to cook, so it gets used almost every day. The oven is a built-in Gaggenau EB375 which came with our house. From what I can tell it was made in late 1987 or early 1988, so it's more than thirty years old. Over the years we have had it fixed by a factory service guy (last convection heating coil replacement was 7 years ago) but now Gaggenau has been purchased by BSG (Bosch Siemens Haushaltgeräte) and they have stopped making parts for it. So I figured it was time to throw it away and get a new one.

But here's the thing. This is a 90cm wide oven, so a big cooking compartment. When we started to investigate replacements, we found that all the modern 90cm replacements have smaller interior dimensions, and fewer operating modes. Our oven is rated for 6.8kW (it uses two separate 230V 16A circuits) and has ten different heating elements that can be used in various combinations. I also noticed the weight: modern replacements are ~50kg whereas the EB375 is more than 70kg. So to cut a long story short, I found a "parts machine" for 30 Euros and two hours of driving, and told my wife I would spend a weekend giving our oven the same treatment that my (purchased very used) workshop machines get.

After wiring it up to see what worked, I tore down the parts machine, to see how it all fit together and to cannibalize the heating elements, thermal cutoffs, relay, controls, etc. (Very nice to work on something that weighs less than I do, for a change.) The sides and back, top and bottom are a made of folded galvanised steel sheet-metal plates, and after you remove them, everything is visible and accessible. By the time I was done with the tear-down, I had the same appreciation I feel when I am inside my 1960s Deckel FP2 or Studer RHU-450, and also understood why these cost so much. The thing was beautifully built, by people who were really trying hard to do everything right. No plastic, no rivets, no snap-fittings that depends upon friction and give. Everything comes apart, it's almost all steel and glass, high-quality stainless steel sheet-metal and threaded screws, ceramic, glass-insulated wiring, spade connectors, robust terminal blocks, and individual components that can be swapped. Perfectly-fitted fiberglass insulation matts encapsulated with IR-reflective foil, held in place with removable tie wires. Very nice redundant grounding design, intended to protect both the user and the oven if parts short or burn out.

Apart from one bit of "high-tech" electronics (a digital time and temperature display) all of the electrical stuff is very simple. A local service company was nice and gave me a labeled schematic and the point-to-point wiring diagram. With the exception of the two main control switches (which are in good shape, ceramic bodies, platinum contacts, with ball bearing rollers on the detents -- and for which I now have replacements) there's nothing there that can't be easily fixed. Two of the three motors (cooling fan, convection fan) are original parts made by the German company EBM, the bearings and coils still look like new. (I have the impression that these class-F fan motors were designed for HVAC applications where they have to run continuously at 100C+ for decades.) A couple of the thermal breakers don't look good to me but still work correctly. Fortunately those are still available from Bosch and not expensive.

A nice thing about having the oven apart is that I was also able to clean it properly. It turns out that the company that made this, Gaggenau, started off in 1683 as an iron casting foundry. Then in the 1800s they became an enamel specialist. This is the process in which you coat steel or cast iron with glass powder, then heat it hot enough to melt the glass so it flows over the surface. It's a small step from there to making ovens. Apart from a few chips in the enamel layer, one day of scrubbing (after I had removed the door, the grill, the inside back, and put the oven on rolling cart) was enough to get it back to "almost like new" shape. But I did ignore the manufacturers warning not to use harsh chemicals and employed everything caustic and mechanical in my arsenal, including oven cleaner, sodium carbonate, lye, paint remover, bleach, brass scrapers, razor blade scrapers, stainless-steel pot scrubbers, and a range of wet sandpaper grits followed by rubbing compound.

The cleaning process involved more than the cooking compartment. In the process of cleaning out 30 years of dust and grease with compressed air, I also discovered that the cooling-air path, which draws in air from below the door, was almost completely blocked by some pretty disgusting grease-soaked dust bunnies. The air is circulated under the (insulated) heating compartment and around the enclosed sides of the oven , then goes up along the inside back of the oven, then returns to the front over the heating compartment and is blown back out the front of the oven via a small gap just above the door. Clearing that cooling-air path should go a long way to keeping the machine running for another decade or two.

In the course of this, just like with my workshop machines, I discovered a whole range of things that had been incorrectly repaired in the past. These ranged from little stuff (a broken clip-on nut inside the door, which I took apart to get to all four glass sides and replace the hinges, a missing steel retention clip inside the temperature control knob) to significant. Some bozo had managed to bend the standoffs which mount the inside back, towards the right side. That meant that the air passages for the convection heating were smaller on one side than on the other. Fortunately I was able to carefully bend the standoffs back to the correct location without breaking them: the steel was soft and malleable. (This completely fixed the main complaint of my family's cooks, that the oven was too hot on one side.) One of the mounting clips for the thermostat sensor probe was broken off, so the sensor was in the wrong position, easily replaced with a clip from the parts machine. I discovered that the convection heating coil was burnt out in part because it was the wrong part: 2600W rather than 3200W, and not an exact fit. That stressed the bottom of the coil where it eventually bent and then shorted and burned through. The top grill heating element was hanging by one corner because someone had broken off and thrown away the welded-on bracket from the other corner, just the mounting screw remained. Easy enough to fabricate a replacement. And so on.

After devoting a weekend to the reconditioning and repair, the oven is looking and working like new, and my wife is happy. A cardboard box of spare parts is going up the attic, after I have finished testing the six thermal switches. The carcass of the old one will go to the recycling center, but only after I've located a replacement 3kW convection mode heating coil and can test it for fit. I'm pretty confident that with a spare for that part also, the oven has at least another decade or two of life in it.

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I wont delete it, as it is too good of a story, but I will lock it so we dont end up with endless stories of oven repairs. Have a great weekend thanks for sharing, bask in the glory that is yours as it will be short lived when the next thing breaks. Ha Ha.

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