Water heater does not start heating; display shows E01 immediately after power-on.

Safety first: Turn off the circuit breaker and close the cold-water supply valve before opening the heater. Confirm no voltage is present with a multimeter.

Steps to check and fix:

• 1. Check water flow: Open a hot tap fully. If the flow is weak, clean the inlet filter/strainer on the cold-water connection of the Kospel heater. Rinse under running water and reinstall.
• 2. Inspect the flow sensor: Remove the front cover. Locate the flow sensor/flow switch on the cold-water inlet manifold. Check for scale or debris; if removable, gently clean the turbine or paddle with vinegar and a soft brush.
• 3. Verify wiring: Ensure the flow sensor connector is firmly seated on the main control board and that wires are not pinched or broken. Reseat the connector.
• 4. Electrical test: With power off, measure the resistance of the flow sensor according to the service manual values. If open circuit or out of spec, replace the flow sensor assembly.
• 5. Control board check: If the sensor and wiring are good but E01 persists, the flow-signal input on the main PCB may be defective. This typically requires replacing the main control board.

If you are not comfortable working with live electrical tests or opening the heater, contact an authorized Kospel service technician.