Water heater does not start at all; display is blank and no lights are on.

Safety: Use caution when working with mains voltage. Turn off the breaker before opening the electrical compartment.

• Check breaker: Verify that the circuit breaker feeding the heater is on and has not tripped. Reset if necessary.
• Inspect power cord and wiring: Ensure that the power cable is intact and that connections at the heater terminal block are tight.
• Internal fuse: Some Buderus units have an internal fuse on the control board. With power off, check and replace with the exact type and rating if blown.
• Measure voltage: Confirm that correct voltage is present at the heater terminals when the breaker is on.
• Control board: If power is present but the display remains dead, the control board's power supply is likely faulty and the board should be replaced.