Safety first: Hot water and steam can cause severe burns. Allow the boiler to cool before opening any panels or bleeding air.

1. Check system pressure and temperature: Read the boiler gauge. Typical hot water systems operate around 12–20 psi and below the high limit setpoint (often 180–200°F).
2. Verify circulator operation: On a call for heat, feel the system circulator pump (e.g., Taco or Grundfos on Weil-McLain systems). It should vibrate slightly and the piping should gradually warm. If it is hot but not pumping, it may be seized.
3. Inspect valves: Ensure isolation valves on the supply and return near the boiler are open. Partially closed valves can cause overheating.
4. Bleed air: Air in the system can stop flow. Use manual air vents or automatic air eliminators to purge air from radiators and high points, following the boiler manual.
5. Reset high limit: Some Weil-McLain models have a manual reset high limit. Press the reset button after the boiler has cooled and the cause has been addressed.

If high limit trips repeatedly, have a technician check pump sizing, flow rates, and control settings.

Boiler shuts down and displays 'High Limit', 'HL', or 'Temperature Limit Exceeded'; may reset after water cools.

Possible Causes