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Houseboat Hot Water System
Designed by Mark Little
Hot Water System Operation
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The Hot Water System (HWS) draws its water from the Murray River from a through-hull water inlet. This is connected to a Shurflo Water pump via stop cock and a filter. From the pump, the water pipe is connected to a water accumulator unit and then via another stop cock to the gas hot water system. The output of the HWS is distributed to various points around the houseboat via another stop cock.

For simplicity, the filters as well as some stop cocks and taps in the hot water piping have been omitted from the diagram below as they do not affect the operation of the water pump or the HWS. Also omitted from the diagram is the cold water diverter connected to the hot water tap in the kitchen, The dirverter sits just before the hot water tap.
When the hot water taps are turned off, the pump pressurises the hot water pipe and then the pump switches off, without any water flowing in the pipes. A lack of water flow through the HWS causes the gas burner to extinguish. Over time, the pressure in the water pipe will gradually fall and the pump will occasionally run for a second to restore the pressure in the pipes.

Maintaining the pressure in the pipes is important, since the water diverter in the kitchen is installed before the tap and the requires a minimum pressure to operate correctly. If the water pressure is too low, the diverter will not operate correctly and it will allow the cold water to run into the river continuously. This will cause the hot water to run, triggering the hot water system, wasting battery power and gas.

When a tap is turned on, the fall in water pressure turns on the water pump and the water flow through the HWS triggering the gas ignition and it starts heating the water. The accumulator contains a water reservoir that can provide water to the pipe when the flow is low so that the pump is not always cycling to maintain low water flows. This makes the flow more even and allows the pump to run cooler under these conditions, When the pressure drops enough for the pump to run, it re-pressurises the accumulator and stops, until the water from the accumulator is used.

When the tap is turned off, the water pressure builds up and the pump turns off. The HWS flame is turned off when the water flow stops.