Display shows E11; heater may heat uncontrollably or not at all.

Safety: Isolate electrical power before working inside the heater.

• 1. Verify sensor placement: Compare wiring to the schematic on the inside of the cover. Ensure inlet and outlet NTC sensors are connected to the correct terminals on the PCB.
• 2. Check sensor types: If sensors were recently replaced, confirm that genuine Kospel parts with correct resistance curves were used. Mismatched sensors can cause E11.
• 3. Inspect wiring: Look for damaged insulation, kinks, or pinched cables. Repair or replace the harness if needed.
• 4. Measure both sensors: At room temperature, measure resistance of both NTCs and compare. They should be similar if they are the same type. Replace any sensor with abnormal readings.
• 5. Control board: If wiring and sensors are correct, the regulation circuit on the main PCB may be defective and require replacement.