Immersion heater gone again.

RAI

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This is the third time in as many years that the immersion heater in my boat's calorifier has developed an internal short circuit. Each time it fails, my multimeter shows the resistance to earth as a few megohms instead of open circuit.
Could it be that there is some form of corrosion that eats a tiny hole in the copper pipe which lets a tiny bit of water in to create the short circuit sufficient to trip the circuit breakers?
Any other possible causes? Any solutions? These little heater elements are silly expensive and a drag to change.
 

VicS

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This is the third time in as many years that the immersion heater in my boat's calorifier has developed an internal short circuit. Each time it fails, my multimeter shows the resistance to earth as a few megohms instead of open circuit.
Could it be that there is some form of corrosion that eats a tiny hole in the copper pipe which lets a tiny bit of water in to create the short circuit sufficient to trip the circuit breakers?
Any other possible causes? Any solutions? These little heater elements are silly expensive and a drag to change.

Different alloys are used for the sheath to suit different water types. Copper, Incoloy or even titanium. Since you will be filling up with water from different locations you should choose Incoloy or preferably titanium. I expect titanium ones are even sillier prices
 

RAI

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Different alloys are used for the sheath to suit different water types. Copper, Incoloy or even titanium. Since you will be filling up with water from different locations you should choose Incoloy or preferably titanium. I expect titanium ones are even sillier prices
Thanks, and I was having trouble finding one that even fits. Is marina fresh water really so corrosive to hot copper?
 

Heckler

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This is the third time in as many years that the immersion heater in my boat's calorifier has developed an internal short circuit. Each time it fails, my multimeter shows the resistance to earth as a few megohms instead of open circuit.
Could it be that there is some form of corrosion that eats a tiny hole in the copper pipe which lets a tiny bit of water in to create the short circuit sufficient to trip the circuit breakers?
Any other possible causes? Any solutions? These little heater elements are silly expensive and a drag to change.
Something strange going on here, mine is 16 years old and still going strong. Has anyone done anything to earthing on the boat?
S
Oh Canaries, is the wiring correct? ie reversed live and neutral? Or something strange along those lines?
 

RAI

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Something strange going on here, mine is 16 years old and still going strong. Has anyone done anything to earthing on the boat?
S
Oh Canaries, is the wiring correct? ie reversed live and neutral? Or something strange along those lines?
Good question, the first one lasted 10 years since the boat is in my possession, probably much older and maybe of better quality than its replacements. The element itself looks symmetric to which terminal is power or neutral and the exterior is earthed. My boat is supposedly double insulated but the immersion heater is the one item which is earthed, supposedly to the pontoon power supply earth.
 

VicS

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Thanks, and I was having trouble finding one that even fits. Is marina fresh water really so corrosive to hot copper?

It depends on the water analysis. Copper is generally suitable for soft water. Incoloy for soft or hard water. Titanium being available for particularly corrosive water.

Worth perhaps checking there's no silly problem with the power supply or heater wiring. Neutral and earth crossed for example.
 

RAI

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Worth perhaps checking there's no silly problem with the power supply or heater wiring. Neutral and earth crossed for example.
I haven't found one, but it seems to be earth leakage that is tripping the circuit breakers. But assuming there is a stray voltage around, how would that corrode a hole / breakdown the immersion heater element's insulation (without tripping to start with)?
 

Tony Cross

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I had a related problem with a new Isotherm calorifier, the welds would leak after only a few months. Isotherm replaced it twice and then I fitted some magnesium anodes inside the tank and the problem disappeared (along with the anodes I might add).
 

RAI

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I had a related problem with a new Isotherm calorifier, the welds would leak after only a few months. Isotherm replaced it twice and then I fitted some magnesium anodes inside the tank and the problem disappeared (along with the anodes I might add).
Thanks, now there is a tip. I must get some magnesium. Thanks. (Dang but they are expensive)
 

David2452

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If it what I an thinking this is something I come across on an almost weekly basis, immersion faults which trip the RCD rather than a short tripping an MCB. Titanium ones are available and dependant on the fitting size can be as low priced as under £30 but if you need a really low wattage one or a small fitting then I'm afraid you are going to pay for it.
 

Hydrozoan

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Particular problems might I think arise (as Vic touched upon in #2) if the composition of the water is variable - in such circumstances, a stable passivation layer of corrosion product may be less likely to form. That might arise if you are often filling at different places with different water characteristics, and/or if your local water is a variable blend of primary sources with differing characteristics (hardness etc.). If the latter is likely it might be worth speaking to a local domestic plumber to see what they experience, and recommend.
 

savageseadog

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My opinion is that differences in earth potentials may give rise to earth currents which will result in electrolysis of the element sheath.You should ensure that the calorifier and the engine is mains earthed.
 

RAI

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Particular problems might I think arise (as Vic touched upon in #2) if the composition of the water is variable - in such circumstances, a stable passivation layer of corrosion product may be less likely to form. That might arise if you are often filling at different places with different water characteristics, and/or if your local water is a variable blend of primary sources with differing characteristics (hardness etc.). If the latter is likely it might be worth speaking to a local domestic plumber to see what they experience, and recommend.
Well, the last one to fail has only seen Canaria Island marina supplied water. A little from Tenerife San Miguel and the rest from La Gomera. The failing element was purchased in Tenerife.
 

RAI

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My opinion is that differences in earth potentials may give rise to earth currents which will result in electrolysis of the element sheath.You should ensure that the calorifier and the engine is mains earthed.
Why the engine? Is part of the circuit that you are thinking of via the calorifier pipes or the cooling water within them. At the moment the calorifier could be outside the boat otherwise - as far as electrical insulation is concerned.
 

Hydrozoan

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Well, the last one to fail has only seen Canaria Island marina supplied water. A little from Tenerife San Miguel and the rest from La Gomera. The failing element was purchased in Tenerife.

OK, so variable water quality is very unlikely to be a contributor. It sounds as if you need to consult a specialist supplier and get the most resistant you can for your size and fitting. Good luck!
 

savageseadog

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Why the engine? Is part of the circuit that you are thinking of via the calorifier pipes or the cooling water within them. At the moment the calorifier could be outside the boat otherwise - as far as electrical insulation is concerned.

The engine is likely to be true earth via propeller etc, mains earth can have a potential difference and yes, currents will flow from one to the other via cooling water. It does raise another issue regarding corrosion of the saildrive and propeller.
 
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