Can a previous landlord foreclose on a house that has been refinanced?

It is unclear why you are using the word "landlord." If you purchased a property, the person you bought it from has nothing to foreclose unless you financed your purchase totally or partially with a loan from the seller ("seller financed" purchase). So, did you sign a promissory note to the seller that is secured by a deed of trust (mortgage) on the property? If so, then the seller could foreclose if you failed to make your payment, just like a bank or other secured creditor. But if the seller signed off on the Settlement Statement and received the full amount designated to him in the Statement, then he probably has no claim against you. However, I cannot give you a definite answer since I cannot see the purchase/sale/escrow documents. You would be wise to obtain a consultation from a real estate attorney, even if you have to pay for it. Your local County Bar Association may have a Lawyer Referral Service that will set up a 30 minute appointment with a specialist in your matter for a nominal fee. It would be money well spent.