Upon arrival customer has a titan tankless water heater that has surpassed its life span. Customer states she will be taking a shower and without warning the water will get cold. We preformed a diagnosis on water heater to find all fixtures are mixing water properly at this time. The only reason you will have a problem with hot water if the heat shuts off while in use. At this time we did not witness unit fail, but water heater will have to be replaced. Titan tankless water heaters have a life span of 6 years and this unit is 11 years old. Titan tankless swap out is sold and customer wants asap installation. Customer put a $750.00 deposit down Thank you for calling John The Plumber -Shane