Furnace will not start at all, no lights or display

Safety: Before resetting breakers, identify and correct any obvious short circuits or burning smells.

Steps:

• Check breaker: Locate the furnace circuit breaker in the panel and reset if tripped. If it trips again immediately, call an electrician or HVAC technician.
• Verify service switch: Ensure the furnace service switch near the unit is in the ON position and functioning.
• Inspect power cord and wiring: Look for loose connections at the furnace junction box. Tighten as needed with power off.
• Internal fuse: Many Buderus controls have a small replaceable fuse. With power off, inspect and replace only with the same type and rating if blown.

If the unit remains dead, the main control board or internal transformer may have failed and requires professional replacement.