According to the installation and servicing instructions manual, “Fault during comfort safety mode”.
Cause of F57
According to the installation and servicing instructions manual. The Ignition electrode is highly corroded
We suggest taking out the ignition electrode to inspect it without opening up the main heat exchanger. The steps for this is to first turn of the boiler. Remove the front panel. Unplug the ignition cable from the ignition electrode including the earth connector. Undo the two screws either side. Remove the electrode assembley. Inspect the electrode and replace as necessary. Please note you will require a new gasket if the existing electrode is fine or it will be included with the new electrode.
Vaillant Electrode 090709