Er:07 tells you the heater is warming the water even though the control module didn’t ask it to. In plain terms, something in the heating circuit is “stuck on.” That usually comes down to either a failing heating element (short to ground) or a control-board relay that’s welded closed.

Start with safety. Unplug the washer before you touch anything. Heating circuits work on mains voltage, and a stuck-on heater can overheat parts quickly if power is left connected.

Now, think about symptoms you may have noticed: the drum warming during a cold cycle, a hot, “electrical” smell, tripped breakers, or the washer stopping mid-cycle and throwing Er:07. All of those point in the same direction—an uncontrolled heater.

The first thing to check is the heating element itself. Pull it for a visual once the machine is disconnected: look for blistering, cracks, burn marks, or any place the coil could contact the metal tub or cabinet. A heater that’s shorted to ground can heat constantly without permission from the control board. When you see visible damage—or your multimeter shows continuity to ground—the fix is simple: replace the heater with the proper Bosch part and new gasket, then reassemble carefully to avoid leaks.

If the heater looks healthy and tests clean (no short to ground, resistance within spec), shift your attention to the control module. Inside is a relay that switches power to the heater. If that relay welds closed, it behaves like a light switch jammed in the ON position. There’s no safe “clean and reuse” here; the reliable repair is replacing the control module. After replacement, clear the code and run a short test cycle to confirm the heater only energizes when commanded.

A few pro tips to keep you safe and save time:

• Always test with power unplugged; only reconnect when you’re ready to run a controlled test cycle.
• If you aren’t used to working with live circuits, don’t. A technician can diagnose a shorted element vs. a stuck relay in minutes with the right tools.
• After any heater or board replacement, check for leaks around the heater seal and verify that cold-wash cycles stay cold.

Bottom line: Er:07 almost always resolves with either a new heater (when it’s shorted) or a new control module (when the relay is stuck). If you’re unsure at any point, calling a professional is the safest way to protect both the appliance and your home.