Boiler powers on but does not start heating when there is a demand from the room thermostat

Safety first: Turn off power before working on control wiring.

Steps to check:

• Verify thermostat settings: Ensure the room thermostat is set above room temperature and is in heating mode.
• Check wiring at boiler: Inspect the thermostat terminals on the boiler (e.g., TA/RT). Tighten any loose wires and confirm correct polarity if required.
• Bypass test: Temporarily bridge the thermostat terminals at the boiler with a short wire. If the boiler starts heating, the thermostat or its cable is faulty.
• Check boiler parameters: Using the Kospel menu, confirm that external control is enabled and correctly configured.

When to call a technician: If the boiler still does not respond with the terminals bridged, the control board or internal relays may be defective.