Display shows E11; heater icon flashes and solution is not warming

Safety: Unplug the unit and allow it to cool completely. The heater block can remain hot after use.

• Inspect heater connections: Remove the side panel to access the inline heater assembly in the solution line. Check that all spade connectors are tight and not heat-damaged.
• Check thermal cutout: Many heaters have a manual-reset thermal cutout button. Press it firmly to reset if present.
• Continuity tests (advanced): With the heater disconnected, use a multimeter to check continuity across the heater element and thermostat. An open reading indicates a failed component that must be replaced.
• Descale if needed: Hard water can cause scale buildup in the heater, leading to overheating. If the heater is partially blocked, replace the heater assembly; do not attempt to drill it out.

Because the heater is a high-wattage component, replacement should follow Stihl specifications and may be best handled by a service center.