Overheating warning alarm

[nigelsweet]

Could anyone help, my 64 astra temperture gauge keeps increasing rapidly, first message service due, then turn off a/c due to overheating, then stop and turn off engine due to over heating and alarm starts ringing. Today the gauge does not reset as before. At this point the gauge rapidly goes from max red to 90 and normal? T Few mile later does the same, felt engine when saying overheating and hoses to radiator and not over hot, any suggestions as to the cause, many many thanks in advance.