Heater displays H11; unit may continue to run but with limited functionality.

Safety: Turn off power before working on low-voltage control wiring.

• Check remote controller: Verify that the remote controller display is on. If blank, check its power supply or batteries (if applicable).
• Inspect cable: Follow the communication cable from the heater to the controller. Look for cuts, pinches, or loose terminations.
• Verify terminal connections: At both ends, ensure wires are connected to the correct terminals as per Buderus wiring diagrams. Tighten any loose screws.
• Test continuity: With power off, test each conductor for continuity and check for shorts between conductors.
• Replace controller or cable: If the cable tests good but communication is still lost, try a known-good controller or replace the cable.
• Restore power and test: Turn power back on and confirm that H11 clears and that the remote controller communicates properly.