Boiler does not start at all, no display or lights.

Safety first: Only competent persons should work on electrical circuits. Isolate power before opening the boiler.

• Check external supply: Verify that the circuit breaker or fuse feeding the boiler has not tripped. Reset once if safe to do so.
• Inspect boiler fuse: Many Weishaupt boilers have an internal fuse on the control board or terminal block. Replace with the same rating if blown, after checking for obvious shorts.
• Test main switch: Ensure the boiler's on/off switch operates correctly and is not mechanically broken.
• Check mains terminal block: Tighten all connections and look for signs of overheating.

When to call a professional: If fuses blow repeatedly or if there is no power despite correct supply, a technician should test the internal wiring and control board.