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On my board I have 2 identical transformers from 230V to 9V. One of them is no longer delivering any current when its input is 230V. The other one functions as expected. I am thinking of putting an extra wire between each of the 9V poles like on the diagram My goal is 2 validate that nothing else on the board is broken. Does my idea make sens? Is there any risk in doing this?

I don't think this is a very good idea. You will be will be using a good transformer to feed a transformer with some sort of internal fault and depending on the fault this could damage the good transformer. A better starting point would be to measure ohms on the primary and secondary windings and ohms primary to secondary on each. Any substantial difference between measurements on the good and bad transformers would indicate a fault. This should be done with all external connections removed.

Thanks, I measured the ohms and noticed a very significant difference. I will then remove the broken transformer from the circuit board. Then I plan to put the wires as in my diagram but without the transformer. Do you see any other reasons not to do this ?

The main thing I would worry about in your plan is the possibility of overloading the transformer. If you try it watch the transformer closely for signs of overheating, (smell, smoke, etc.). If all seems ok run it for an hour or so then feel it. If it doesn't burn your fingers it's probably ok. Another thing to think about is the possibility that two 9 volt windings were originally used because they are at different voltages above ground. If this is so you haven't much choice but to replace the defective transformer.