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Hot water too hot

Our engine gives us 'free' hot water but it gets scaldingly hot. Is it possible to regulate the temperature, e.g. With a thermostat? What would be involved in altering the system?

Asked by: Paul Taylor  | 12.19pm, Wednesday 1 July

WW says:

This is understandably an issue- the calorifier temperature will reach engine operating temperature in most boats. However, you don't want to directly reduce the temperature of the hot water cyolinder (calorifier)- as reducing that to a sensible level (such as 45 to 60 degrees celcius) would mean that the calorifier would be at risk of being a legionella source.
The easiest way to achieve a sensible hot water source is a blending valve on the output of the hot water cylinder, which is very easy to fit. While you are at it, you might consider fitting an expansion tank here (in addition to the one that is normally present on the cold water side) as this helps reduce expansion stress on the calorifier (if the pressure relief valve has to operate, then the cylinder is being stressed as the water expands as its heated).
However, this does mean that the hot water pipework will be at reduced temperature, which could lead to it becoming a legionella source of infection- so you might consider a more frequent disinfection regime of the hot water system.
alternatively (and better practice) you could fit belnding valves immediatley belwo each hot tap, which blend hot and cold water together to an acceptable temperature, while still allowing very hot water along the pipework, keeping infection levels low. I would still fit the additional expansion tank though.

Mark Langley  | 3.34PM, Wednesday 1 July

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