Q: "Why aren't my warehouses sending goods to each other?"

Warehouses are only allowed to match when they have a combined priority of 3 or higher. Eg. 2/1 or better. This is higher than other matches and is designed to ensure that warehouses don't just constantly send goods forwards and back between themselves.

If you set a warehouse to "Empty" then it will always place an OUT offer of priority 2 when it has storage capacity and vehicles available. If you set a warehouse to "Fill" then it will place an IN offer of 2 when it has storage available. "Balanced" will alternate between 0, 1 and 2 depending on storage levels.

If your warehouses are placing IN/OUT offers that when matched would be 3 or higher then they will be allowed to match in the algorithm, if they aren't matching then something else must be stopping them. Quite often it is because the OUT warehouse has used up it's vehicles so check that it still has some vehicles available when checking for the match. If you are finding this is the problem then it might be a good idea to turn on "Reserve cargo trucks for local delivery" as this will limit the number of trucks that can be used for exporting.

If there is enough trucks available then it may just be that there is something closer that is matching instead. You could try turning on "Warehouse First" which will adjust the distances in the algorithm to make the warehouses seem closer together and hence more likely to be chosen to match with each other.

If they still don't match then I would suggest looking on the Pathing tab of the Issues panel (CTRL+3) to see if either warehouse appears on the list.

Finally if none of that works, then there is a new option called "Improved Inter-Warehouse Transfer" which allows matching at lower priority but checks storage levels as well which you could try to see if it resolves the issue for you.

Note: There is now a new setting in the global settings "Improved Inter-warehouse Matching" which applies a bit more smarts to warehouse transfers that you could also try.