Boiler shows E3 and shuts down shortly after starting

Safety first: Allow the boiler to cool before touching piping or components. High temperatures can cause burns.

• Check system temperature: Read the boiler temperature gauge. If it is near or above the high limit setting (often 180–200°F for hot water), the high limit is doing its job and shutting the boiler down.
• Verify circulator operation: When there is a call for heat, feel the circulator pump body. It should vibrate slightly and get warm. If it is cold and silent, check the pump power connection and any pump relay on the control board.
• Inspect valves: Ensure all supply and return isolation valves near the Pennco boiler are fully open. Check any zone valves for proper operation.
• Reset high limit: Some high limit controls have a manual reset button. With power off and boiler cooled, press the reset if present. If it trips repeatedly, do not continue resetting—find and correct the cause.
• If circulator runs and flow is good: The high limit aquastat or sensor may be defective and reading incorrectly. Replacement of the high limit control or sensor should be done by a technician.