Thermostat shows E15 and indicates valve or actuator error; the connected zone does not heat correctly.

Safety first: Turn off power to the wiring centre before working on actuator connections. Actuators may become hot during operation.

Steps to diagnose and fix:

• 1. Identify affected zone: Use the thermostat or wiring centre indicators to determine which zone/actuator is causing the E15 error.
• 2. Inspect actuator wiring: Open the wiring centre and check that the actuator wires are correctly connected to the zone terminals and firmly clamped.
• 3. Test actuator resistance: With power OFF, disconnect the actuator and measure its resistance. Compare to Danfoss actuator specifications. Infinite or near-zero readings indicate a fault.
• 4. Verify actuator type and settings: Confirm that the thermostat or wiring centre is configured for the correct actuator type (normally closed or normally open). Incorrect configuration can be interpreted as a fault.
• 5. Replace faulty actuator: If the actuator is defective, remove it from the manifold or valve body and install a new Danfoss-compatible thermal actuator. Follow manufacturer torque and installation guidelines.
• 6. Clear error and test: Restore power, clear E15, and command heat to the affected zone. Confirm that the actuator opens and the zone heats.

When to call a professional: If you are not familiar with underfloor manifolds or hydronic systems, a heating installer should replace actuators.