Your boiler has lost internal communication between its main control parts, meaning it cannot properly send or receive instructions to run your heating.

No communication via EMS BUS connection: 1. Check the HMI plug on far right of the PCB (low voltage connection). 2. If using the Key: Check the Key connections (black, white, red, green) are plugged in to the correct position on the PCB. (Next to orange BUS connection leaving one space.) Check the pins on the plug. 3. Check the bridging links are in LR & 230 V out. 4. Replace the board. 5. Occasionally the Key connection (green flap) can cause this. 6. Check the 230 V external wiring does not run alongside the BUS connections.