Boiler does not start heating; display shows E01 and heating indicator does not light

Safety first: Switch off the boiler using the main power switch and isolate it at the circuit breaker. Allow the unit to cool before opening any covers.

Steps to check:

• Verify system pressure and valves: Ensure the heating system is filled to the recommended pressure (typically 1.0–1.5 bar for many Kospel boilers) and that all isolation valves on the flow and return are fully open.
• Bleed air from the system: Use radiator bleed valves and any automatic air vents near the boiler to remove trapped air that may prevent the flow switch from activating.
• Inspect the flow switch/sensor: Remove the boiler front cover (following the Kospel service manual). Locate the flow switch or flow sensor on the inlet side of the heat exchanger. Check for debris or limescale restricting movement. Clean gently with a soft brush and reinstall.
• Check electrical connections: Inspect the wiring harness from the flow switch to the main control board for loose plugs, corrosion, or damaged insulation. Reseat connectors firmly.
• Reset and test: Restore power, reset the boiler according to the user manual, and open a heating demand. If E01 persists after cleaning and bleeding, the flow switch/sensor may need replacement.

When to call a technician: If you are not comfortable opening the boiler casing or measuring continuity on the flow switch, contact an authorized Kospel service technician.