Boiler display shows A71; unit may lock out on safety chain fault.

Safety: A safety device has opened for a reason. Do not bypass safety switches for operation.

Steps:

• 1. Identify safety devices: Locate the high limit, rollout switch, flue spill switch, and any other safeties wired in series to the control.
• 2. Check manual reset devices: Some rollout or high limit switches have a small reset button. After the boiler has cooled, press each reset button once. If a device immediately trips again, shut the boiler down and investigate the cause (blocked flue, flame rollout, overheating).
• 3. Inspect wiring: Follow the safety circuit wiring. Look for loose spade connectors, broken wires, or corrosion.

If A71 remains after verifying all safeties are reset and wiring is intact, a faulty safety switch or control board input may be present. Have a qualified technician test and replace components as needed.