Hot water ..... no water !!!

Bav34

Bav34

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Our boat gets its hot water from two sources .... shore power and from the engine. The engine is a Volvo 2020 which is fresh water cooled and I guess then that the calorifier transfers heat into the hot water tank through the pipes that I can see. Not too bothered about the mechanics of that.

My question is, what happens if I mistakenly run the boats fresh water tank dry (apart from a bollocking from the wife /forums/images/graemlins/ooo.gif ) ?

If on shore power I guess the system trips as the element is trying to heat air not water but what if you are motoring along and run out? Does the hot water that runs from the calorifier through the pipes into the now empty tank just keep circulating or is there a danger of something overheating?

Thanks Steve.
 
At present mine is drained, no problem with running the engine I just leave the tap's open and pump off. I would'nt use the 240 though!
Most calorfiers have a pressure relief valve, has yours?
 
No water...no problem...

There isn't a problem if you run out of water, there'll be no damage to the calorifier. The plumbing of calorifiers is arranged so that pressurised cold water enters low down, and heated water leaves higher up. If you run out of fresh water, you can't pump anything in to the calorifier but it'll still have water in it. If you're motoring, the hot water from the engine just circulates as normal - it can't do any harm. If you're on shorepower, the immersion heater element will still be in water, not in air.
 
I think you will find that, similar to a domestic hot water tank, the hot water is drawn from the top via an internal pipe for a horizontal calorifier and consequently you will not empty it by running out of water, you will just not be able to push the hot water out by pumping cold in - if that makes sense!

Barry
 
Thanks, not sure about the relief valve but there is definitely an electrical trip just as we have on the boiler at home. We always drain the freshwater off for the winter and I was going to give the engine a trial run this morning but didn't due to the sudden thought about overheating something. Sounds as tho' that wouldn't have been a problem if there is always water in the 'hot' tank. Thanks for the advice.
 
cannot think why you would think that warmish engine water would damage the copper coil of a calorifier.
i drained my calorifier down for winter, but ii have ran the engine as lets face it if the heating element destroys itself at engine water temps it can't be much good.
 
Tyce, perhaps I haven't explained it well. The hot water tank supplies VERY HOT water ....not 'warmish', and this is surely fed from a very hot engine, therefore if I let the hot water tank run dry my concern is that the VERY HOT pipework going into a now empty tank (i.e. not filled with cold water) could cause damage.

Clearer?
 
It won't be a problem. When the calorifier is full the water in it eventually approaches the temperature of the engine coolant. This is why it can sometimes be sensible to have a blender on the hot water output of a calorifier as an anti-scald precaution. If the calorifier is drained (which can be difficult if there's a NRV in the feed from the supply tank) then the coil still can't get any hotter than the coolant so there's not really much difference.

The immersion heater shouldn't be switched on, of course. This can sometimes be damaged before the thermal safety cutout trips if it's not immersed!
 
ooohhh temper,
maybe i did not make myself clear, how hot do you think water - yes water can get in a engine, even if pressurised.
it will heat the calorifier up to exactly the same temp as the engine water eventually if no water is drawn.
so stop worrying it aint gonna melt
 
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