Boiler displays E15 and locks out, often with very high temperature reading

Safety first: Turn off power and allow the boiler to cool completely. Do not reset an overheat device until the cause is identified.

• Locate manual reset limit: Many Utica boilers have a manual reset high limit or safety thermostat on the heat exchanger or supply header. Look for a small red button on a disc-type control.
• Check system flow: Verify that the circulator pump is operating and that all zone valves or isolation valves are open.
• Reset device: Once the boiler is cool, press the red reset button until it clicks. If it immediately trips again on the next call for heat, shut the boiler down and investigate further.
• Inspect for restrictions: Check strainers, filters, and the heat exchanger for signs of blockage or scale. Flushing or descaling should be performed by a professional.