Another immersion question

cast_iron

robbie7730 wrote: »

The amount of heat required would be massive to be conducted down the very low element CSA to the immersion base which is in very good contact with the water. And we would see a lot more flooded houses, as burnt connections are not unheard of in immersion elements.

I tend to agree, but what else could have caused the massive heat build-up. Some sort of massive heat build up definitely occurred to melt the plastic cover, and it also travelled up the flex to indent the tank insulation.

Any chance the live and neutral cables somehow came into contact but didn't manage to trip the fuse? Is the immersion on an RCD?

Regardless of a dodgy solder joint, the source of the heat build-up needs to be ascertained. A bad connection seems like the most likely answer to this question.

Bruthal

cast_iron wrote: »

I tend to agree, but what else could have caused the massive heat build-up. Some sort of massive heat build up definitely occurred to melt the plastic cover, and it also travelled up the flex to indent the tank insulation.

Any chance the live and neutral cables somehow came into contact but didn't manage to trip the fuse? Is the immersion on an RCD?

If the 20 amp MCB failed, then either the main CU fuse would go, or the fault would blow clear. The RCD is unlikely to trip on a live - neutral contact anyway.

Them plastic covers can distort from having them covered with towels etc as the immersion head gets quite hot anyway, not saying that caused this, but just mentioning them plastic covers distort from heating easily enough.

Regardless of a dodgy solder joint, the source of the heat build-up needs to be ascertained. A bad connection seems like the most likely answer to this question.

Nothing much can be ruled out alright. A very bad solder joint maybe could be compromised by the normal heating of an immersion element. But if a properly soldered setup cant take the heat of a bad connection (which is not unheard of in immersions) which now has to conduct this heat down the element end and to a solder joint and metal base being cooled by the water, how can it take the heating from the 3kw heating element itself? Even in the cold water, you would be unable to touch them elements as they get very hot at their surface in the water. And would probably heat the metal base they are attached to more than any loose connection can.

If i just seen this without much evidence i would say the element was switched on dry. But i would say its clear thats not the case now.

I think about 750 watts (25% of rating) or so is the max heat that can be generated by a loose connection in a 13 amp (3kw) load. A fair bit of heat that can melt the cover no problem. So its conceivable this could of badly damaged the top cover and wiring of the immersion fitting alright. So maybe that did melt the solder. All i can say is how does it not happen more often so, if this element in question was soldered properly?

Maybe they should braize them if this is a possibility.

cast_iron

robbie7730 wrote: »

If the 20 amp MCB failed, then either the main CU fuse would go, or the fault would blow clear. The RCD is unlikely to trip on a live - neutral contact anyway.

I was hinting at if there was an MCB at all. It could be an old style setup, with DZ fuses. With that much heat, a live-earth fault could have occurred also and hence the lack of RCD could play an extra roll. Pure speculation, mind.

I think about 750 watts (25% of rating) or so is the max heat that can be generated by a loose connection in a 13 amp (3kw) load. A fair bit of heat that can melt the cover no problem. So its conceivable this could of badly damaged the top cover and wiring of the immersion fitting alright. So maybe that did melt the solder. All i can say is how does it not happen more often so, if this element in question was soldered properly?

That's why I'm just thinking it's maybe a bit further up the line. The OP will prob blow that theory out of the water though.

Bruthal

cast_iron wrote: »

That's why I'm just thinking it's maybe a bit further up the line. The OP will prob blow that theory out of the water though.

If it was a live neutral short, or live earth, the heat at the point of contact could be high, especially if there is a few ohms resistance there, but if there are no protective devices behind the short, the short would quickly be expected to blow itself clear.

If it was a hard low resistance/impedence direct short, then the heat dissipated would be along the entire circuit from the CU, and not concentrated in the immersion unit.

If it was indeed a bad connection in the circuit at an element end, this will be in series with the 18 ohm bath element for the worst case scenario, and so the highest heat output from a bad connection would be where the bad connection roughly equals the elements own 18 ohms, so 36 ohms total, with the element giving off 750 watts, and also the bad connection. But the bad connection would be a very concentrated 750 watts, while the element would be spread over its length, in the water. So in this scenario maybe it is remotely possible for a bad connection on the element end to cause the outcome seen by the OP.

Any lower, or higher resistance in this connection results in its 750 watts being reduced. Lower resistance and the element outputs more, higher and both the bad connection and the element output less. But even 300 or 400 watts from a very localised point maybe could do the damage described here.

The element end with the bad connection you would think would have its solder joint fail first through direct conduction if this loose connection did cause it, and then as water comes through, no more joins fail maybe.

It must be an extremely unusual one anyway. I never would of thought a loose connection could heat the immersion metal head enough to do this due to its massive heat sinking properties with water contact. But maybe it has in this case. And after calculating the roughly 750 watts in theory possible from a loose connection onto a 3 kw element, maybe it is feasable.

meercat

just to get away from an electrical fault
any chance your boiler caused this problem by building up pressure and releasing steam into cylinder causing plastic cap to melt after blowing a hole in the thermostat sheath and let water flood out?
check your expansion pipe in attic

meercat

meercat wrote: »

just to get away from an electrical fault
any chance your boiler caused this problem by building up pressure and releasing steam into cylinder causing plastic cap to melt after blowing a hole in the thermostat sheath and let water flood out?
check your expansion pipe in attic

No, the manufactures have already accepted it's a build up of heat under the head of the immersion due to a loose neutral connection, their description not mine, I just don't understand it:o also I would be an expert on heating systems although now I'm more of a expert on the correct use of a wet/dry Hoover.

Bruthal

gary71 wrote: »

No, the manufactures have already accepted it's a build up of heat under the head of the immersion due to a loose neutral connection, their description not mine, I just don't understand it:o also I would be an expert on heating systems although now I'm more of a expert on the correct use of a wet/dry Hoover.

Even though i was saying in theory a loose connection feeding a 3kw load can dissipate up to 750 watts max, it is hard to see such a connection lasting very long at anything like that wattage in such a small area such as a loose connection. The connection would likely just dissintegrate. And again, why do they insist it was on the neutral? if it was a loose connection, there is no more reason why its on a neutral than a live terminal. And why do we never see it happen on other immersions?

You should ask them this.

robbie7730

robbie7730 wrote: »

Even though i was saying in theory a loose connection feeding a 3kw load can dissipate up to 750 watts max, it is hard to see such a connection lasting very long at anything like that wattage in such a small area such as a loose connection. The connection would likely just dissintegrate. And again, why do they insist it was on the neutral? if it was a loose connection, there is no more reason why its on a neutral than a live terminal. And why do we never see it happen on other immersions?

You should ask them this.

On a new install last year a immersion was found smoking, the suppliers received a report on the installation after a investigation by the manufactures and it was found a loose neutral was at fault and they are telling me it's the same thing again, I am going to chase up the original report to explain this funky fault and I'll post it if I get it.

Bruthal

gary71 wrote: »

On a new install last year a immersion was found smoking, the suppliers received a report on the installation after a investigation by the manufactures and it was found a loose neutral was at fault and they are telling me it's the same thing again, I am going to chase up the original report to explain this funky fault and I'll post it if I get it.

Yea i wouldnt be surprised to see one smoking or melting its plastic cap etc from loose connections, i just never would of thought it could melt the solder. but just because one of their immersions failed at the neutral connection, they assume its the neutral again?

I never even noticed they were soldered at that point, although when you mentioned it earlier it did seem familiar alright having solder in that area on some of them. Its just hard to see the solder thats in contact with the water getting hot enough to melt even from a severely burning connection under the cap, unless there was a problem with the solder as well as the loose connection.

I think water has been known to seep up through the element insulating material when the outer copper jacket of the actual elemen splits in the water. It seeps up and out at the element ends under the cap. Nothing to do with this of course.

This whole thing is certainly worth keeping a good note of.

yoshytoshy

Sorry for replying late to this ,but I've seen this happen before. The water ended up coming from the soldered connection on the immersion ,because it overheated.
Someone wired the immersion wrongly and the homeowner left the immersion on while gone on holidays ,so the stat didn't kick in (don't know why the overheat didn't)

I left the old immersion with her as proof ,some builder had installed the cylinder as part of an attic conversion.

Bruthal

yoshytoshy wrote: »

Sorry for replying late to this ,but I've seen this happen before. The water ended up coming from the soldered connection on the immersion ,because it overheated.
Someone wired the immersion wrongly and the homeowner left the immersion on while gone on holidays ,so the stat didn't kick in (don't know why the overheat didn't)

I left the old immersion with her as proof ,some builder had installed the cylinder as part of an attic conversion.

Standard immersion heaters dont seem to have overheat cutouts in them.

If the bath wire is connected to bath as an example, and sink one to neutral on a single stat immersion, now the 2 elements can actually come on in series when bath is selected, at about 1.2kw output, and the stat wont switch them off. Is this similar to what mistake was made, or did you see what was done?

yoshytoshy

robbie7730 wrote: »

Standard immersion heaters dont seem to have overheat cutouts in them.

I think nearly all the pre-installed immersions have the little pop-up stat in the middle. I don't know if the one I seen was a pre-installed ,because I was so shocked at seeing the solder leaking. :eek:

Bruthal

yoshytoshy wrote: »

I think nearly all the pre-installed immersions have the little pop-up stat in the middle. I don't know if the one I seen was a pre-installed ,because I was so shocked at seeing the solder leaking. :eek:

Did you notice how it was connected, i edited the above post to show what mistake can be made, bath wire connected to bath in switch, sink to neutral(or sink wire to sink, bath to neutral), now you can have 2 elements in series with the stat not turning them off.

yoshytoshy

robbie7730 wrote: »

Did you notice how it was connected, i edited the above post to show what mistake can be made, bath wire connected to bath in switch, sink to neutral(or sink wire to sink, bath to neutral), now you can have 2 elements in series with the stat not turning them off.

I found the problem at the immersion switch ,the neutral was in the wrong spot alright. I didn't get too into it because I'm a plumber and my job was to fix the leaking immersion.
I left the old immersion there ,the girl had only got her house redecorated:(

Bruthal

So if you get the flex, and black is bath, brown is sink, and blue neutral for example....

Connect black to its correct bath terminal in switch. Connect brown to neutral of switch, and connect blue to the sink terminal in switch, both elements come on when bath is selected, and output 1.2kw, and worst of all, the stat does nothing.

When sink is selected, it works properly with stat controlling it.

The above is one possibility of incorrect wiring so the single stat immersion continously heats, and the stat has no effect when bath is selected.

Similar if sink is correctly connected to sink of switch, bath to neutral, and blue to bath terminal.

Bruthal

yoshytoshy wrote: »

I found the problem at the immersion switch ,the neutral was in the wrong spot alright. I didn't get too into it because I'm a plumber and my job was to fix the leaking immersion.
I left the old immersion there ,the girl had only got her house redecorated:(

Yea looks like that so, if the neutral of the flex is connected to one of the bath or sink switch terminals, then the stat will be out of the circuit, depending on which of the bath or sink cores is connected to the neutral, and what position the bath/sink selector is in, and the water will boil once the switch is left on.

I remember immersions years ago where the brown was actually the neutral. Im sure it was, maybe someone else will remember that?

I always double check what core is connected to what points in the immersion unit when fitting and connecting one.

yoshytoshy

robbie7730 wrote: »

So if you get the flex, and black is bath, brown is sink, and blue neutral for example....

Connect black to its correct bath terminal in switch. Connect brown to neutral of switch, and connect blue to the sink terminal in switch, both elements come on when bath is selected, and output 1.2kw, and worst of all, the stat does nothing.

When sink is selected, it works properly with stat controlling it.

The above is one possibility of incorrect wiring so the single stat immersion continously heats, and the stat has no effect when bath is selected.

Similar if sink is correctly connected to sink of switch, bath to neutral, and blue to bath terminal.

I've seen immersions wired wrongly before a few times ,they bubble like mad and steam is in the attic when left on. But I've never seen solder melting before ,maybe they don't make the immersions like they use to:(

People don't know their immersion is wired wrongly ,unless they forget to turn off the immersion

EDIT: I've also seen Gary's problem on shower switches ,switches melted because of a bad connection.

yoshytoshy

robbie7730 wrote: »

I remember immersions years ago where the brown was actually the neutral. Im sure it was, maybe someone else will remember that?
.

Theres still loads of old immersions with the old braithed cable Three browns and an earth.