Boiler shuts down with 'Flue Temp High', 'Stack Temp', or similar; may reset after cooling.

Safety first: Allow the boiler and vent to cool before touching flue components.

• 1. Check system flow: Verify all zone valves and isolation valves are open and circulators are running. Low water flow can cause high flue temperatures.
• 2. Inspect heat exchanger (visually): Look through inspection ports for heavy soot or scale buildup on the heat exchanger surfaces. This requires professional cleaning.
• 3. Verify venting: Ensure vent length and diameter match Weil-McLain specifications. Excessive restriction can raise flue temperature.
• 4. Sensor check: Inspect the flue temperature sensor wiring for damage or loose connections.

Cleaning or descaling the heat exchanger and verifying combustion settings must be done by a trained technician.