Legal Question in Real Estate Law in California

The HOA probably can go back on the deal. Here's my analysis:

First, the e-mail and your express or tacit acceptance of it did not form a contract between you and the HOA in the ordinary sense, even though contracts are usually formed by offer and acceptance, because there was no consideration on your side. Nevertheless, there is a legal principle called "promissory estoppel" which can cause an enforceable bargain to be reached even in the absence of consideration. Promissory estoppel says that a promisor will be estopped (barred) from denying his obligation to another when that other has relied to his detriment on the promise. The reliance must be reasonable and must result in a detriment to the one who relied upon the promise and is seeking to enforce it.

Here, although you have bought and paid for hardware, this sounds from your own set of facts like something you were going to do anyway, whether or not the HOA paid half or all of the door replacement. Therefore, I don't see that you have suffered a detriment. (Your future detriment of having to pay 100% doesn't count; the promise was apparently retracted before that).

In addition, the HOA might also argue that your reliance was unreasonable, because you have a set of their rules and regulations and should already know they can't pay the full tab. I don't know if this is a strong argument or not.

There may be other facts that swing the balance in your favor (or the HOA's), but based on what's given I don't think you would win if this went to court. I might add that Small Claims judges are not always predictible (or knowledgable) and you might win anyway.