novel - When do you stop "pushing" a book?

Let's suppose you have finished your novel, through all the appropriate stages of drafting and editing needed. You begin submitting the book to various agents and/or publishing companies, but none of your queries gets answers.

I'm talking about a worst-case scenario, where you either get copypasted replies or no reply at all, and no feedback about how your work could be improved.

Given this grim setting, when do you stop, if ever, sending queries for that particular novel? Is it safe to assume that it's either badly written or there's no market for it? Do you keep it in a locker and try to publish it again years later?

Edit: To be completely clear, I'm not in this situation right now, but I figure it's an interesting question to ask.

Answer

Never give up a book based SOLELY on the response to your queries. The reason is that the response rate you get to queries tells you relatively little about your book's quality. Query writing is its own form of writing, and one that it is highly rewarding, but surprisingly difficult to master. It's quite possible that a good book could have bad queries. So, as @Amadeus has correctly noted, your first step should be to improve your query-writing game. There are plenty of good books and online resources on this topic. Until you get a query accepted, you haven't received any direct feedback about your book at all.

With all that said, there are some valid reasons for rejecting a query that do connect to the book. First, an unprofessional query usually indicates an unprofessional writer, which indicates an unprofessional book. Any errors at all in a query --typos, bad grammar, and so forth --are usually disqualifying in this regard. Second, a weak or vague query often means that the writer doesn't actually know what his or her own book is about. That can mean a vague or confused book. Third (to be harsh) a badly written query can mean a bad writer --or at least one who hasn't achieved a high standard of work yet. Finally, an unmarketable query typically means an unmarketable book. This is the least fair one, because it has nothing to do with book quality, but publishers are in a business, and if they can't figure out who your audience is, and why that audience would buy your book, they aren't going to publish you.

So my advice to you is twofold: Work hard at improving your queries AND use that process to understand where corresponding weaknesses in your book might lie. Do you understand your own book? Do you know your target audience? Do you know the market? Is your book flawlessly edited and free of errors and typos? Is there something compelling about it? Only if those answers are all coming back as negatives (and you can't fix them) should you consider tabling this project and starting a new one.