Accumulator tank or not?

I was kind of hoping that was an error. 90C water is very, very dangerous.

Any calorifer with no thermostatic control can reach this kind of temperature if you run the engine hard enough, for long enough.

Some boats have a mixer valve to keep the HW tap below 55 or so degC. Some of these valves don't work terribly well when the hot water is at a much higher pressure than the cold.... Which may happen if the HW side lacks expansion space.
 
My Beta operates with the cooling water temp at 90 degrees once warmed up. When I connected the calorifier to it it gets to 88 degrees as heat is lost to the pipes and calorifier, but it does mean the calorifier water gets heated to 88 degrees. I do have an adjustable mixer on the calorifier and initially it was set high so water came out scalding. I have an NRV and know the water expands as once hot the first time I use it I can run the hot for a few seconds off the expansion tank before the pump kicks in.
 
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