Boiler displays E8 and shuts down; may be accompanied by gurgling sounds in the heat exchanger

Safety first: Turn off power and allow the boiler to cool completely. Hot water and surfaces can cause severe burns.

• Verify system flow: Ensure all isolation and zone valves are open. Confirm the circulator pump is running during a call for heat.
• Bleed air: Air trapped in the system can cause localized overheating. Bleed air from high points, radiators, and automatic air vents.
• Check strainers: If your system has a Y‑strainer or dirt separator, clean it to restore flow.
• Consider descaling: If the boiler is older or on hard water, the primary heat exchanger may be scaled. Chemical descaling should be performed by a professional following Ruud procedures.
• Reset and monitor: After restoring flow, reset the boiler and monitor supply temperature. If E8 recurs, the outlet sensor or heat exchanger may need replacement.