Producer items, such as cleaning sets, spawn new items when you tap on them. However, these producer items have certain capacities and go into cooldown/charging mode after emptying.Please tap on the item and check the info text box above your game board to see how long you need to wait to spawn new items.
You can wait until their cooldown periods end or use your gold to skip the waiting times.
Learn more about Mergedom: Home Design merge puzzle game.