B

System pressure is very or extremely low. This is triggered when the pressure falls to between 0.6 and 0.3 bar. Top up water until the target pressure is reached.
Filling loop
▶ Vent the heating system and top up water until the pre-set pressure reached.
Pressure sensor
▶ Check the continuity down harness for the pressure sensor and replace if required.
▶ Check the voltage at the pressure sensor and replace if required.