There are many benefits that a mortgage refinance can have for a homeowner. However, if just one thing is wrong, or one mistake is made, it can cost you a lot of money, and put your home at risk. Here are 4 of the most expensive mistakes a homeowner makes when mortgage refinancing.1) Not Getting Mortgage Interest Rates Locked InMortgage rates change frequently. In the time it takes to process and approve your refinance application, interest rates probably have changed a few times. Once you find a mortgage rate and lender you like, ask them to lock it in. If this is not done, you may find that when it comes to signing day, the interest rates on your home loan refinance have changed. Ask your mortgage lender to put it down in writing and sign it. They will usually only do this if asked to, and they will set a limit of no more than 4 business days on the interest rate.2) Not Comparison ShoppingIf you were not aware, there are literally hundreds of mortgage lenders. If you were Each lender is different, and while the services are typically the same, the fees, rates, and qualifications for each one may differ greatly. It is always recommended that a homeowner looks at a variety of different mortgage lender and banks to get the best deal possible.3) Refinancing a Mortgage Too OftenRefinancing a mortgage to get better interest rates and save some money is a great decision. However, some homeowners take it overboard and refinance every time interest rates drop. However, while this may seem like a good idea, it is not. Refinancing a mortgage too often will result in massive fees, closing costs, and extended mortgage terms. Getting a mortgage refinance too frequently is often a bad idea for the long run.4) Unknown Break In Length.Many homeowners do not realize that there are fees and costs associated with getting a mortgage refinance. Calculating the time it will take to recoup the costs, and start seeing savings, needs to be known and anticipated.Here is a quick example of how to. Say you are going to save around $300 per month on your mortgage refinance. However your closing costs are $3000. That means it will take 10 months until your break in period.These tips should help homeowners avoid some of the common costly mistakes that are made.