What does the error code "L.E."mean on an isar HE24 combi boiler?

Some times when the boiler is running on central heating,the cut out opperates and L.E.flashes.Nothing works untill the reset is pressed and then all works normaly for about a 12 to 18 hours.The system water pressure is about 1 bar and no leaks.We have a remote timer set for early morning and evening.Before I call out a qualified engeneer I would like to know what the problem is likely to be.I have not been able to find this error code on any site or manual.
Cheers
Peter