Achieving safe, reliable hot water

I do enjoy a hot shower in my boat and my current vessel, a Trusty T23 displacement motorcruiser, heats the water from the engine up to at least 80°C and it can also achieve a similar temperature from the electric immersion heater when solely on shore power.

There are three taps on the boat: one in the cockpit, one for the kitchen sink and one in the shower. The first