Thermostat shows 'CF' or 'CAL' and does not control heating until calibration completes or fails.

Safety: Let radiators cool before handling TRVs.

• Wait for completion: If 'CF' appears briefly, allow the calibration cycle to finish. Do not remove batteries or disturb the valve during this process.
• Check batteries: Install fresh batteries before starting calibration to avoid mid-cycle failure.
• Verify adapter: Confirm that the correct Eurotronic adapter ring is used for your radiator valve type and that it is firmly tightened.
• Free valve pin: Remove the TRV head and manually move the valve pin in and out until it moves smoothly. Reinstall the head and restart calibration.
• Replace drive: If calibration fails repeatedly, the internal motor or position sensor may be defective. Replace the TRV head.