Boiler shuts down shortly after firing, display shows “Err 2” and burner cycles off on high temperature

Safety first: Turn off power before opening the control compartment. Hot water and surfaces can cause burns; allow the boiler to cool.

• Check system pressure and temperature: Look at the boiler gauge. Normal residential hydronic systems typically run 12–20 psi when cold and under 30 psi hot. If pressure is very low, the boiler may overheat locally.
• Verify circulator operation: When there is a call for heat, feel the circulator pump body (Taco, Grundfos, etc.). It should vibrate slightly and get warm. If it is cold and silent, check the breaker, service switch, and wiring to the circulator relay on the Burnham control.
• Open valves and purge air: Confirm all supply and return isolation valves near the boiler and zones are fully open. If some radiators or baseboards are cold, bleed air from bleeder valves until water flows steadily.
• Inspect high limit control: On boilers with a mechanical aquastat (e.g., Honeywell L8148/L7224), verify the high limit setting is appropriate (typically 180–200°F). If the boiler trips at much lower temperatures, the sensor or control may be faulty.
• Clean heat exchanger (visual): Remove the burner door and visually inspect the cast iron or stainless heat exchanger sections for heavy scale or soot. Excess buildup restricts heat transfer and can cause rapid temperature rise. Cleaning should be done by a professional with proper brushes and vacuum.
• Reset and test: Restore power, reset the control, and monitor operation. If Err 2 recurs quickly, have a technician test the high limit sensor and circulator amperage.