Can't say I know the inside of the Lombard too well so I might be well and truly off the mark here but is there any sort of thermal sensor that's tripping (or in this case not tripping) and controlling when the fan comes on and off? If that's borked (or just not sensing properly for whatever reason) then the machine wouldn't know it was overheating, wouldn't know to turn the fan on and yadda, yadda, yadda...or it could be something else entirely

Just a thought