Steam boiler stopped working with above fault indicated. Thanks to our resident expert @DavecUK, he was able to guide me through problem solving. Turned out one of the boiler’s sensor wires had parted. Had me puzzled why this might have happened and then realised that the bracket, each time the panel was opened to refill the tank, was brushing against the edge of the spade connector on one of the two sensor wires.
Dave guided me on the best type of connector to go for and happily the problem is fixed.
If you have an Evo, might be a good idea to check to see if yours has the potential for developing the same problem.