My oil furnace is leaking water from the underside,due to expansion because of freezing, can I fix it myself?

Yes if you can weld.My oil furnace is leaking water from the underside,due to expansion because of freezing, can I fix it myself?
That's not much to go on. Is it a hot water furnace or a steam furnace? Water usually leaks on the bottom due to gravity. You need to find out where the actual leak is and what is leaking and you also have to repair the cause or it will happen again.My oil furnace is leaking water from the underside,due to expansion because of freezing, can I fix it myself?
If your water jacket is cracked from freezing you have a problem. Have someone come in to give you an estimate on a new one and at least you'll find out if it's trashed.