Calorifier question

[cynthia]

Merve is in Greece working on getting the boat ready for the summer. One unexpected job is the replacement of the hot water exchange unit, so this is his question:

I'm in the process of replacing the domestic hot water calorifier on my 2001 Bavaria 34. The one I have taken out (original equipment fit - make unknown) has the outlet for the pressure relief valve plumbed back into the freshwater tank. The instructions for the replacement unit I'm fitting (Isotherm SLIM 15) states that the outlet from the pressure relief valve should be left open and unobstructed (stating that it should not drain into seacock or even a skin fitting) it also states that some water will always be present at this outlet in normal operation. I like the original Bavaria solution rather than having to drain water into the bilges. Are Isotherm just being overcautious here or I am I missing a trick ? ie can I plumb the new unit in the same manner as the original Bavaria one ? The only difference appears to be that the Bav pressure relief valve operated at 4bar and the Isotherm one not until 7bar.

Your help, as always, is much appreciated!

 

[vyv_cox]

I suggest that the logic is as with a domestic cistern overflow. It draws your attention to the problem before it becomes a major issue. I cannot think of another reason for not doing it. The higher pressure of the new RV should ensure that the old solution will work well, assuming the valve ever lifted, which ideally it should not.

 

[Hadenough]

I would also guess that they are concerned about legionellis. Introducing hot water into a stored cold water system may allow bacteria to grow. Although the risk from the hot water system the way most boats are used is a far greater risk in my view.

 

[Trundlebug]

I would also guess that they are concerned about legionellis. Introducing hot water into a stored cold water system may allow bacteria to grow. Although the risk from the hot water system the way most boats are used is a far greater risk in my view.

I don't think that would be a major consideration.

Legionaire's disease only a problem from atomised sprays, not taps. The only such source on a boat would be a shower head.

Also, Legionella bug needs dirty water with crud to hide behind, ideally in a recirculating system, and a nice constant temperature of 20-65 degrees to breed in.

Calorifier has (or at least should have) clean water in, replaced regularly by fresh (cold, sub 20 deg C unless in the height of summer) water, and may sit for months in cold conditions. Not ideal conditions overall for the bug to live, so not a likely risk although it's always good practice to keep shower heads clean even at home.

I think the main thing the calorifier supplers are worried about is any chance of restricting the outlet. When it blows, it needs to blow freely to save the calorifier bursting. Any pipes and hoses attached could get kinked or restrict the flow - and you wouldn't know until it happened, then it would be too late.

All IMO.