Boiler shows E13 and locks out; may be associated with outdoor reset operation

Safety first: Turn off power before working on low‑voltage wiring.

• Locate outdoor sensor: Typically mounted on an exterior north or northwest wall, away from direct sun.
• Inspect wiring: Check the cable from the sensor back to the boiler for cuts, staples through the wire, or loose connections at the control terminals.
• Test sensor resistance: Disconnect the sensor and measure resistance. Compare to the Ruud chart for the current outdoor temperature. Replace if readings are out of range.
• Verify polarity and terminals: Ensure the sensor wires are on the correct outdoor sensor terminals and not mixed with thermostat or pump wiring.