On demand water heater with two heaters in series and a flow rate detector controlling one of the heaters

摘要

Disclosed is a method of operating an on-demand water heater, the water heater including a first heater in series with a second heater and a flow rate detector controlling at least one of said first or second heaters. The method includes the steps of detecting the initiation of water flow; turning the first and second heaters on each at maximum power; detecting when the outlet flow of water reaches a predetermined temperature threshold; monitoring the water flow rate; and detecting whether the water flow rate is below a low flow threshold. When the water flow rate is below the low threshold, the first heater is turned off by the controller.