Airdale TCU unit alarm Broke probe / not connected

Hi all

We have Airedale TCU's on various sites and have a couple of units now and again alarming on probe broken / not connected, the unit resets and will work fine for anywhere from 1 week to 6 months we have changed the transducer and also replaced the cable for the controller and we still get the fault but only on 2-3 units out of about 40. only thing we haven't changed is the PCO controller but can't see it being the controller, i'm thinking it might be a software issue so wondering if anyone on here has come across this issue on airedale units?