gzt: There is no maximum deposit. Someone at the bank is going to look very silly.
This is correct. In fact it’s ridiculous - there’s no such thing as a deposit that’s too big. If that was the case, the bank could be guilty of trying to lend you more than you need which is unethical and against banks’ codes of conduct. I suspect you have spoken to someone at the bank who doesn’t know what they’re doing - or there’s been a misunderstanding.
Having a high deposit is very much to the borrower’s and the bank’s advantage. It puts the borrower in a lower risk category and gives the bank more opportunity to offer you a discounted home loan rate because their bad debt provisioning is much lower. Banks actually like people with high deposits.