Customer called in about water only getting mild warm. Upon arrival saw that water heaters are plumbed in in a series. The secondary water heater is down. Primary water heater only 6 years old. Due to how water heaters are plumbed in, secondary water heater water is cold and only gets fed hot water from primary water heater. Will need to replace water heater or remove from the system. Gave customer options and customer opted to go ahead and get water heater replaced along with new expansion tank and prv. Customer would also like water heaters to be plumbed in parallel so both heaters are being used at the same time. Will return tomorrow morning to install.