Machine does not heat water or steam, display shows E03 and brewing is blocked.

Safety first: Unplug the machine. The heating circuit operates at mains voltage and can retain heat; do not touch the thermoblock until it has cooled.

Step-by-step:

• 1. Confirm symptom: Try to start a hot water or steam function. If the machine immediately shows E03 and water remains cold, the heater is not energizing.
• 2. Visual inspection (advanced): Remove the top cover. Locate the thermoblock and follow the thick heater wires back to the control board. Check for burnt connectors, discoloration, or loose spade terminals.
• 3. Check for tripped thermal fuse: Many Siemens thermoblocks have a thermal cutoff or thermostat attached. Inspect for signs of overheating or a physically blown fuse. Do not bypass a thermal fuse; it must be replaced with the correct Siemens-rated part.
• 4. Electrical testing (for qualified persons only): With the machine unplugged, use a multimeter to measure resistance across the heater terminals. An open circuit indicates a failed heater. Also check continuity through the thermal fuse.
• 5. Professional repair: Replacing the thermoblock or heater assembly requires disassembly of hydraulic and electrical connections and should be done by a Siemens service center to ensure safe operation and leak-free reassembly.