Got bit of problem.... Evangeline (1985 1.6 TD) had hot flush the other night

whilst standing on the drive, cooling fan cut in (at top speed and very noisy) for no reason

hadn't been driven for 24 hrs so nice and cool. Disconnected battery, fan stopped, re connected no fan

so intermittent problem maybe? Have left battery disconnected for moment. Has anyone else had this happen??? Any suggestions please?
