Boiler will not fire and indicates 'Limit Open', 'Safety String Open', or similar; multiple safeties are wired in series.

Safety first: Do not reset any safety device until the cause is identified and corrected. Turn off power and gas before inspection.

• 1. Identify all safeties: Refer to the Weil-McLain wiring diagram to locate rollout switches, blocked vent switches, high limits, and other safeties in the limit string.
• 2. Check for tripped rollout or blocked vent switch: These often have a small reset button. If tripped, investigate for signs of flame rollout, soot, or vent blockage before resetting.
• 3. Inspect wiring: Look for loose or broken wires between safety devices and the control board. Repair any damaged conductors.
• 4. Reset only after correction: Once the underlying issue (e.g., blocked flue, dirty burner) is addressed, press the reset on manual devices and restore power.

If the limit string continues to open, a professional must evaluate combustion and venting for safety.