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Just when you think you've done all the stupid things it's possible to do on a boat


Neil2

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I got back to the boat today to discover I had left the immersion heater switched on all day.  And the cold water tank was virtually empty.  It is a relatively small tank (250 litres) and was well under half full this morning.   I've never had an immersion heater on a boat before, but I presume the storage tank has been merrily chucking hot water out of the expansion pipe whilst being refed with cold water until the cold water tank ran dry.  Now, in a house this obviously can't happen as the storage tank is topped up from the mains.  On a boat however I'm not sure what the scenario is when the hot water tank is no longer receiving a supply of cold water, as I suspect mine wasn't at some point this afternoon.  

 

I know what happens to the element in a kettle when you try and use it without sufficient water (I've done that enough times) and I wonder if the hot water cylinder reaches a point where a similar situation occurs ie the immersed element is no longer immersed and dies.  

 

At the moment I haven't run off enough hot water to know if the immersion still works - I wonder if anyone has idea what damage may have resulted from my stupidity. 

 

 

 

 

 

 

 

 

 

Edited by Neil2
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Cylinders and calorifiers fill from the bottom and empty from the top so will always be full. So you emptied the cold tank, the pump has run on without water? Battery flat? oh, no, you must be on the shoreline. 

If you managed to boil off the water until the element was exposed, it will just burn out. Where did all the steam go?

Does your heater not have a working thermostat?

Edited by Boater Sam
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Sam - yes on a shoreline and I also left the battery charger on.  Yes my immediate thought was the thing must have a stat but if it has it doesn't stop the water getting so hot it flows out of the expansion pipe.    

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2 minutes ago, Neil2 said:

Sam - yes on a shoreline and I also left the battery charger on.  Yes my immediate thought was the thing must have a stat but if it has it doesn't stop the water getting so hot it flows out of the expansion pipe.    

Do you not have an expansion vessel on the hot water system?

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Difficult to believe that 50+ litres have been expelled through the PRV. You say the cold tank was well under half full and now virtually empty, perhaps not that different? probably the only damage done is to your wallet, check your electricity meter! 

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16 minutes ago, TheBiscuits said:

Do you not have an expansion vessel on the hot water system?

No it just goes straight over the side.

 

1 minute ago, grahame r said:

Difficult to believe that 50+ litres have been expelled through the PRV. You say the cold tank was well under half full and now virtually empty, perhaps not that different? probably the only damage done is to your wallet, check your electricity meter! 

My thoughts exactly Graham and I'm hoping the tank wasn't completely dry, I'll happily take the hit on the meter over a new immersion element..

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24 minutes ago, Neil2 said:

No it just goes straight over the side.

 

My thoughts exactly Graham and I'm hoping the tank wasn't completely dry, I'll happily take the hit on the meter over a new immersion element..

what about the water pump, was that running dry?

 

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All a bity puzzling as immersion heaters usually have not only a thermostat but an overheat protection thermostat too.

 

So leaving it ON all day should just have resulted in nothing worse than a nice pleasant tankful of hot water when you got home, and a biggish electricity bill.

 

 

 

Edited by Mike the Boilerman
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Thinking about this, either your water pump is set to too high a pressure or your PRV is faulty.

 

What *should* have happened is your calorifier PRV should have vented maybe a litre or two of hot water overboard to relieve the pressure, then just sat there hot with the immersion kicking in and out on the thermostat to keep the water at about 80 degrees. 

 

If your calorifier constantly pumps hot water overboard when the immersion heater is on there is something wrong with the system.

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My immersion has been on constantly for the past few days, as is always the case if I'm onboard at my mooring.  There has never been the slightest issue, it doesn't spit water out of the PRV, and I have instant access to replenishing hot water.  The electricity use is not excessive either.  Maybe there's a few pence to be saved by faffing about heating the tank, turning the immersion off, then heating the tank again in advance of next time you need hot water, but I doubt it's much as the Surecal calorifier tank is pretty well insulated. 

 

It wasn't as "stupid of you" as you think to leave it on whilst you went out, so stop beating yourself up.  You have a design issue or a fault - this problem has helped you discover that and once it's sorted all will be well, you'll have reliable hot water, and you'll know more about your boat. :)

 

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14 hours ago, grahame r said:

Difficult to believe that 50+ litres have been expelled through the PRV. You say the cold tank was well under half full and now virtually empty, perhaps not that different? probably the only damage done is to your wallet, check your electricity meter! 

Oh no it's not!

Happened to me while cruising.

PRV failed completely

Rear bilge filled completely,

overflowed into engine bilge (which happened to be spotlessly clean)

Only spotted by the Management who saw clouds of steam - water vapour

Pumped excess water into the cut and popped into to Those Nice People known to Mr Smelly who gave me a spare PRV that they had knocking around.

 

NOW I CHECK AND ROTATE THE PRV 'REGULARLY' and carry a spare - thus "guaranteeing" that it will never fail again.....

 

Edited by OldGoat
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1 hour ago, Sea Dog said:

My immersion has been on constantly for the past few days, as is always the case if I'm onboard at my mooring.  There has never been the slightest issue, it doesn't spit water out of the PRV, and I have instant access to replenishing hot water.  The electricity use is not excessive either.  Maybe there's a few pence to be saved by faffing about heating the tank, turning the immersion off, then heating the tank again in advance of next time you need hot water, but I doubt it's much as the Surecal calorifier tank is pretty well insulated. 

 

It wasn't as "stupid of you" as you think to leave it on whilst you went out, so stop beating yourself up.  You have a design issue or a fault - this problem has helped you discover that and once it's sorted all will be well, you'll have reliable hot water, and you'll know more about your boat. :)

 

My immediate reaction - and it was immediate when I started the thread - was that on a boat these things are less sophisticated than domestic hot water systems, and I was an idiot leaving the immersion switched on.  I'll investigate further to see if there should be a stat and take it from there.  It's a bit ironic all this because we hardly ever use a land line, it's only because we are stuck on the Lancaster canal and got fed up of cruising up and down constantly. 

 

As it is I seemed to have got away with it, the immersion still works I guess the tank was right on the dregs when I got back.

 

 

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2 hours ago, Sea Dog said:

My immersion has been on constantly for the past few days, as is always the case if I'm onboard at my mooring.  There has never been the slightest issue, it doesn't spit water out of the PRV, and I have instant access to replenishing hot water.  The electricity use is not excessive either.  Maybe there's a few pence to be saved by faffing about heating the tank, turning the immersion off, then heating the tank again in advance of next time you need hot water, but I doubt it's much as the Surecal calorifier tank is pretty well insulated. 

 

It wasn't as "stupid of you" as you think to leave it on whilst you went out, so stop beating yourself up.  You have a design issue or a fault - this problem has helped you discover that and once it's sorted all will be well, you'll have reliable hot water, and you'll know more about your boat. :)

 

Exactly this. When I go in a marina such as last winter I switch the immersion on when plugged in to the mains and switch it off just before I unplug again days weeks or months later. The thermostat does its job, always hot water and a similar principle to leaving a fridge on permenantly when it's down to temperature.

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53 minutes ago, Mike the Boilerman said:

 

I find it hard to imagine how a simple spring loaded PRV can fail completely. Did the spring break perhaps? Or was it not a conventional spring operated PRV?

FWIW - it was a conventional PRV as fitted by the good, the bad and the ugly. Some years ago - thus the memory fades. My recollection was that it jammed open (somewhat calcified - my bad in not checking). There certainly was extra pressure as a result of the  engine heating a cool calorifier. The accumulator is on the pump side of a NRV which is / was normal practice (?)

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2 hours ago, Mike the Boilerman said:

 

What usually happens is the work correctly and dump a load of water when the system pressure rises too high, and the PRV gets the blame for the high pressure fault. 

Too true! The PRVs are usually 3 Bar, which is about 43 p.s.i., close to the cut out pressure of many pumps. I watched one installation where the pump would exceed the PRV pressure just as it cut out. PRV would open, about half a pint of water would shoot out, and the pump would start again for a couple of strokes. Repeat ad infinitum! (There wasn't an accumulator on that system) 

1 hour ago, OldGoat said:

FWIW - it was a conventional PRV as fitted by the good, the bad and the ugly. Some years ago - thus the memory fades. My recollection was that it jammed open (somewhat calcified - my bad in not checking). There certainly was extra pressure as a result of the  engine heating a cool calorifier. The accumulator is on the pump side of a NRV which is / was normal practice (?)

It is normal practice for an accumulator, as many (especially horizontal) calorifiers have an NRV on the cold water feed. Fitted like that, it will not function as an expansion vessel, though. With no NRV fitted, an accumulator on the cold feed will double up as an expansion  vessel, and may be enough to prevent venting through the PRV.  Probably not best practice, as there is the possibility of hot water back feeding the cold system.

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2 hours ago, Neil2 said:

My immediate reaction - and it was immediate when I started the thread - was that on a boat these things are less sophisticated than domestic hot water systems, and I was an idiot leaving the immersion switched on.  I'll investigate further to see if there should be a stat and take it from there.  It's a bit ironic all this because we hardly ever use a land line, it's only because we are stuck on the Lancaster canal and got fed up of cruising up and down constantly. 

 

As it is I seemed to have got away with it, the immersion still works I guess the tank was right on the dregs when I got back.

No you are not an idiot.

You should be able to leave the immersion on and  the heater should cut out when the set temperature is reached .

Keep a  look/listen out for hot water being expelled and the water pump pulsing occasionally   . ........ which should not ordinarily happen. I have been hooked up to shore power for days with the immersion on full time  with no issues.

Does the water get scalding hot? 

 

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