5L - BUS-Communication fault

What does 5L mean?

This fault indicates a problem with the communication between the boiler and the control unit (thermostat). It can occur if connections are poor, cables are damaged, or if the control unit itself is faulty.

• Dirty or corroded connection terminals at the control unit or boiler
• Faulty control unit (thermostat)
• High resistance or damage in the connection cable between the boiler and the control unit
• Defective electronic board (PCB)

Click steps to track your progress.

1. 1

   Switch off the boiler and cut the main voltage supply. Check the connection terminals at both the control unit and the boiler for dirt or corrosion. Clean them if necessary and reconnect the cable.

2. 2

   Remove the control (thermostat) and restart the boiler to see if the error persists. If the error disappears, the control unit may be faulty and needs to be replaced.

3. 3

   Check the connections and the cable between the control unit and the boiler for high resistance or damage. If damaged, replace the connection cable.

4. 4

   If the issue persists after checking connections and cables, the electronic board (PCB) might be defective. Turn off the boiler and cut the main voltage supply before any further action.