Opel Insignia hot engine start problems

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.

One of the most common causes of non-starting when hot would be the Engine Coolant Temperature sensor. Though it may not produce any codes, it can cause flooding or insufficient fuel being injected into the engine. Have it tested.

So, you have a "no crank" problem, not a "crank, no start".

You will have to test for power arriving at the small trigger wire of the starter when the key is held in "start" position. You can't test it unless the problem is present.

Diesel and petrol driven engines are different and same symptoms could be due to different causes.

Waiting is not going to get you any answers and if any, it might not apply.

When engine fails to start, you need to check if the injectors are firing. A faulty fuel cut solenoid fault can result in no fuel getting past the fuel punmp to the injectors.

Did you check for trouble codes?

You would have to perform testings to find out what is causing it.

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