Jonny, I'm going to point you to a website. This is not to be intended as a "Read a book, lepton!" answer - I hate those. From your questions I'm sensing a general lack of understanding of the brewing process so this is intended to give you basic knowledge, not as criticism. John Palmer has put his entire first edition of "How to Brew" online. Here's the link:
http://www.howtobrew.com/
The number one thing is that homebrewing is relatively easy. Each of us do it somewhat differently but key is relax and have fun at it. Armed with a bit of knowledge, you'll be making fantastic beers in pretty short order but it does take that bit of knowledge.
If you're doing all-grain BIAB (Brew in a bag), one of the simplest causes of low gravity would be simply that you didn't get all
Thanks
Please can you clarify what you mean here? It's very confusing to me - the kit instructions say to recirculate once. eg, sparge with sparge water, then take the wort and pour it over the grains again, once. Would you suggest otherwise?
How could you recirculate wort before sparging? I thought the re-circulation kind of is the sparge?
I think you just told us your problem. First, the nature of the questions you're asking hint that you may not know a lot about the brewing process - you don't seem to know what each step is doing and why. This isn't a critique, we've all been there. So I'm going to recommend a website:
www.howtobrew.com
It's the entire first edition of John Palmer's "How to Brew" and it's where a lot of us got started. Sorry if this appears to be a "read a book, noob" answer - I hate those, they're not the norm for Brewer's Friend and don't want to come across as arrogant. It'll give you some of the basic knowledge you need to feel confident that you're at least doing the right thing.
Sparging rinses the sugars from the spent grain and should be done with clear water. The procedure here would be to do your mash in a bag or strain the wort after mashing - either way the goal of that step is to remove the grain from the wort. I believe the procedure then asks you to pour your sparge water over the grains. This will rinse any remaining sugar from them. Recirculation, taking the wort and pouring it back through the grains until it's relatively clear, seems difficult if not impossible with this setup. If you did pour the wort back through the grains after your sparge step, you added back sugar to the spent grain, taking it out of the wort, which could account for your lowered gravity.
Here's where knowing the terminology counts. Recirculation in brewing (also called by its German name, Vorlauf) is a step prior to draining the mash or sparge: Before running it into your kettle, you drain off wort and pour it back through the grain bed to clarify it. When the wort is relatively clear, then you start running it into your kettle. This may not be practical for your kit so what I'd do, I'd get the first wort and the sparge wort in a vessel, let them settle for a while, then pour the clear wort off, leaving the gunk in the bottom.