If your zipper on the Ensuite tent (or any other product, for that matter) seems broken, there might be an easy way to fix it:
As a bit of general advice that applies to all tents, when pitching your Ensuite tent make sure that the doors are zipped close, so that you avoid stretching the tent too much when pegging down which puts a lot of stress on the zipper during opening and closing.
The zipper teeth don't lock together
If your teeth on your zip are popping off, try lightly clamping down on each wing of the slider with a pair of pliers to increase the zipping pressure.
The zipper keeps catching
If you notice that your zipper is catching and the slider is not moving smoothly along the zipper, you can try applying some lubricant to the teeth. Silicone Spray is best (not oil based), but if you don't have it handy around the house you can also use a bar of soap, a candle or a Lead Pencil by running it along the zipper.