How can I baking multiple procedural materials into one image texture?

I am trying to bake a set of procedural materials into a single texture for some assets i am creating.
The kettle has 5 materials applied to the different sections of the object and the model is a single object with layed out UVs.
I have created a duplicate bake target and a blank texture to bake the diffuse to.
However each time i bake i only get a grey area and none of the reds, blacks or silvers.
Can someone tell me whats the best way to make multiple procedural materials onto a single image texture.
I am baking from selected to active and the Bake target has a material with an image texture selected to bake to.

How looks like the target model, is it a lowpoly version of your teapot? Or is it an identical copy?

Btw you have to add the image (the texture you are baking into) to every of your material nodes setup at bake target object (if there is more than one).

edit: also try to swap the order of the objects selection (selected vs active), maybe you made a mistake there

I have tried putting an copy of the texture image in each of the material set ups and made sure they are the active node. i have also tried active to selected and just a single model as the models are identical.
the only but i can get to bake is the grey fill gauge on the kettle no matter which material or model i have selected.
im very confused on this as i have followed a tutorial on this and i cant see that im doing anything differently.
the biggest thing i dont understand is why it is only baking out the grey part.

It’s metallic. I don’t think metallic has a diffuse component. It’s like baking a glossy shader to diffuse.

I normally just plug the metallic color into a diffuse shader to get that baked, and then I’ll make a metallic map, normally using a roughness bake. But the process translates well from blender to ue4.