Tankless water heater replacement services cost $2,290 on average, but the typical range is between $1,183-$3,399. The cost to have your tankless water heater replaced varies depending on a few factors including what kind of water heater you’re installing as well as the labor costs for removing the old unit and installing the new one. For some tankless water heater replacement services, the costs can reach as high as $4,800+ if the water heater you choose is a particularly expensive model.