The furnace will not start at all; there is no display or lights on the Weishaupt controller.

Safety: Do not work inside live electrical panels. If you are unsure, call an electrician.

Steps:

• Check breaker: Locate the furnace circuit breaker in your electrical panel. Reset it if tripped. If it trips again immediately, do not force it—there may be a short circuit.
• Main switch: Ensure the furnace's main power switch, located near the unit, is in the ON position.
• Fuses: Some Weishaupt controls have internal fuses. With the power off, a technician can check and replace blown fuses with the correct rating.