UK Car Repair: astra 1.7td hard start when warm, crank sensor, test purposes

Question
when car is warm difficult to start replaced temp sensor and new relay but car starts fine when i disconnect temp sensor took to garage for diagnostics on computer said no rpm was told crank sensor faulty  would this affect my car this way also why is it when i disconnect the temp the car starts fine  
PS car starts fine when cold no problem

Answer
The car would not start at all if the Crank sensor was bad! So first. find another more experienced garage! Your diagnostic process was better than theirs. As you did change the temp switch there are only a few possibilities.  I suspect that the computer is at fault, the temp switch gives a signal to the computer which in turn varies the mixture strength.  I presume, when you changed the switch, you topped up the coolant and, that there was actually coolant up to the switch recess?  If this is the only problem I wouldn't worry to much about it as you have found out how to overcome it. The only sure answer would be to change the computer, probably an expensive item,  It would be nice if you could find someone with the same model so that you could do the switch.  Most shops who work on these cars have a good used unit for test purposes, or, they have a another car with which to do the trade.  In my garage we would wait until we got an identical car in, then call the owner