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I would start off by checking the timing belt to make sure the tensioner has not failed.
The fault code is for the electrically operated thermostat, which is in the valley under the intake manifold.
The only way to know would be to drop the pan, but it won't cause these symptoms. It's more common on the 1.8t Passat due to the high heat of the turbo pulling that heavy vehicle.
You need to remove the upper plastic timing covers at each side.
If the timing is far off it will set a fault, but I hope you didn't leave it running for long if it was making a lot of noise.