Holden Astra 2000 ECM light on high teperature advised to replace with new computer replaced computer 12 hours later ECM light on again advised to flush system problem fixed was it really the computer?

Thats like saying that my monitor went bad so now i have to replace my whole computer... No the computer was never the problem, either the coolant was going bad or the temperature sensor was. Before you spend that kind of money again get a second opinion. And always try the easiest and cheapest option first for repair, sensors and antifreeze are easy and cheap compared to the engine control module.