Replacing "short wire" in immersion heater

[boilingpoint]

Hi,

This morning, I found that my immersion heater had stopped working. The short wire that runs from the thermostat to the live terminal of the heater had fried (or at least its insulation did) and disconnected from the terminal pin.

Although I've scavenged a replacement wire from an old immersion heater, there's no obvious way of attaching it. (The heater came with the wire permanently fixed in place.)

Is it safe to solder the wire to the terminal pin? Any other options?

In the photo, it's the pin with the blue base.

 

[ShaunCorbs]

New immersion heater sorry to say

 

[boilingpoint]

New immersion heater sorry to say

Thanks. Why do you say that?

 

[ShaunCorbs]

You can’t repair them easily and not worth it as the repair won’t be as good

 

[boilingpoint]

Thanks, but again more information would help.

Trekking up to Screwfix in the middle of winter at the height of a pandemic, buying a new heater and going through the rigmarole of fitting it is easier than soldering?

There's no doubt it won't be as good. The question was: is it safe?

Another option I've come across is using a high temperature ceramic block attached to the pin.

 

[ShaunCorbs]

Yes much easier than soldering it as it’s spot welded from manufacturer

no wouldn’t be safe as it’s got to hold / withstand 15 amps

and no to the ceramic block

also they don’t snap for a reason so either it’s physical damage or it’s component damage eg over amping

 

[Murdoch]

Buy a new immersion ..... and no the ceramic block ideal isn’t a good idea either.

 

[boilingpoint]

OK. Thanks, both.

As I found it, the wire was fried (the insulating sheath was burnt and crumbled away) and was either free or hanging by a strand (it came away from the terminal easily).

When tested, the heater shows the correct resistance (just under 20 Ω) as does the thermostat. The heater is copper and only three years old. A couple of days ago, I adjusted the thermostat temperature (downwards) and all seemed fine.

Any idea what might have caused the wire to burn up? Is there any chance it could be external? The last thing I want is to go to the trouble of replacing the heater only for it to happen again.

 

[ShaunCorbs]

If it’s crispy it’s either current draw or bad connection probe / thermostat end

 

[Murdoch]

Poor connections are normally the cause of what you have

 

[John.g]

I have replaced a number of these that have failed on the connections to that hi limit stat, I think you can now buy the element with a combined control&hi limit stat, you just replace the entire stat if any failure.

 

[John.g]

In view that the element is checking out OK resistance wise and is only 3 years old why not replace the existing stat with a combination dual safety stat which has the usual adjustable control stat and a non adjustable over temperature stat, just measure the existing stat length before purchasing, far easier than replacing the whole element.

 

[Gasmk1]

If it’s crispy it’s either current draw or bad connection probe / thermostat end

possibly when you the wire had a loose connection in the stat causing it to arc occasionally seen this burn out wires before

 

[boilingpoint]

Thanks, ShaunCorbs, Murdoch and Gasmk1.

That sounds fairly conclusive. It's possible I could've nudged the wire when adjusting the thermostat. It's frustrating because every time I wire up the thermostat, I always make sure it's screwed tight. Don't know what else I can do.

Not sure, but I think I read something yesterday about the temperature changes due to the water heating and cooling cycle causing the grip on the wire to weaken over time.

Thanks, john.g. The thermostat I think you're referring to, with the safety pop-up button, is what I have. It wasn't overheating of the water that was the cause. (The water was lukewarm.) Even if I just replaced the thermostat, I'm still left with the same problem: it's not possible to safely reattach the short connecting wire to heater's live terminal pin. The whole heater needs to be replaced.

 

[Ric2013]

Yes much easier than soldering it as it’s spot welded from manufacturer

no wouldn’t be safe as it’s got to hold / withstand 15 amps

Hi Shaun,

My feeling is that you are right and that it will not be possible to get a better connection that the original spot weld, unless it was originally defective. That said, I'm also wondering why a 15A porcelain connector (assuming it fits) would not work. I'm assuming that this part gets hot and the porcelain may not take the heat?

Agree soldering would not work.

Or are we just saying that we cannot advise the OP on how to cobble something like this since it's a repair to a factory-made part, so whoever modifies the design by introducing an additional connexion needs to take responsibility if it later goes wrong (and we aren't electrical engineers)?

 

[ShaunCorbs]

Both chances are you wouldn’t get a good enough connection from the post also you wouldn’t be able to put the lid on

 

[steadyon]

1. While the porcelain would probably take the heat, the constant expansion and contraction would almost certainly cause the screw to go loose fairly quickly.
2. If you had the equipment you could silver solder the cable to the element connector. Ordinary solder won't do, it couldn't take the heat of any arcing at the contact point or nearby.

 

[w0z]

Can you get a better photo of the weld from the side. If you're going to attempt to solder it the existing would need to be filed down to clean bare metal to get any chance of a decent joint that would last, and it would have to be wrapped with tinned single core and soldered over for added future stress-proofing. Does the bit that's sticking out look like you could drill a very small hole in it?
Also silicone wire insulation would be required (or better still you could heatshrink it afterwards with a couple of layers.) It's not going to be easy to solder and it will act as a heatsink so will be difficult to get it to temperature.