After you replaced the regulator it is possible that you have traped air in the engine block.Try to let some water out of the regulator hoses as it is running some times you will here air come out as you pull on the hoses don't get burned if the water is hot. If that does not work it is possible that you have a blockage in one of the fittings the water must flow in and out of the regulator through the engine block hope this helps.