Thermostat display shows E01 and heating does not start even when there is a demand for heat.

Safety first: If you need to access the receiver near the boiler, switch off power to the boiler and receiver at the circuit breaker before removing any covers.

• Check receiver power: Verify that the Delta Dore RF receiver (e.g. Tybox RF receiver module or Tybox 5100/5200 receiver) LED is lit. If not, check the boiler’s fused spur or breaker and restore power.
• Reduce distance and obstacles: If the thermostat is far from the receiver, temporarily move it closer (if it’s a wireless Tybox/Tybox 5100 room unit). Test if E01 clears. Avoid placing the thermostat behind metal cabinets, near large appliances, or on reinforced concrete walls.
• Eliminate RF interference: Turn off or move away other 868 MHz RF devices (alarm hubs, RF gateways, some smart meters) and Wi‑Fi routers placed directly next to the thermostat or receiver. Retest.
• Re-pair the RF link: Put the receiver into pairing mode (press and hold the PROG/PAIR button on the Delta Dore receiver until the LED flashes), then follow the thermostat menu: Menu > Settings > Radio / Pairing and confirm pairing. Wait for the E01 code to disappear.
• Check antenna orientation: On some Delta Dore receivers with an external antenna, ensure the antenna is vertical and not coiled or pressed against metal pipework.

If E01 persists after re-pairing and moving the devices, the RF receiver module may be defective and should be replaced by a qualified technician.