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AskAsk

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grumbler

If this happens ONLY when the heater is ON, then 100% it's the heater's fault. Full stop.

Is the heaters' power the same as of the replaced ones? 

Jeepers_Creepers

AA, what actually trips - is it the individual MCB that's dedicated to the immersion circuit, or is it the main RCD?

Does only ONE breaker trip, or does the whole (or half) the house power go off?

Myser

What was the original fault to require both immersion heaters to be replaced?

Given that the MCB and RCD are tripping would indicate a Live->Earth fault.  The circuit should be tested by an electrician to rule out a fault with the fixed wiring.

Myser

can they really be faulty from new or has dynorod broke them when they installed them?

If they are new, then they might not have been wired correctly.  Did the electrician check how they were wired or only confirmed the fixed wiring?

If you have the report from the electrician confirming the fault with the immersion heaters and that the circuit checks out OK, then forward it to DynoRod.

Myser

It's possible if the immersion heaters have a thermostat separately wired in, that they haven't been wired properly.  Can you post a close-up photo of the immersion heater's wiring?

Jeepers_Creepers

Hi AskAsk.

Your initial issue was that both elements didn't function for whatever reason, most likely that they'd burned out. They simply did not heat, but they also didn't 'trip' anything.

With the replacements, the issue is that they trip the main RCD when powered up, and that - as said before - indicates an 'earth leakage' usually from the Live to Earth (I understand that touching Neutrals to Earth can also cause RCDs to trip on certain systems?). The new elements do NOT trip their own MCB, so that suggests it isn't an actual 'short-circuit' of any degree in the wiring - ie the Live and Neutral wires are not touching.

What can cause two new elements to 'leak' like this? Only two things I can think of - one is that they were inherently faulty such as allowing a slight ingress of damp inside the element casing (both?! Unlikely.), or the other is that they were bent beyond an acceptable limit most likely during installation. Excessive bending would damage the electrical-insulation layer inside the casing, so the 'Live' element wire running in the middle is able to leak electricity to the earthed casing.

Yes, your sparky is able to test just the elements on their own for such leakage - he simply disconnects it from the supply wires and runs an insulation test on the actual item.

If your sparky is confident of his findings, could he put it in writing so you can hold Dynobodge to account? You simply give them an ultimatum in writing - sort it by replacing the elements, or else you'll employ a plumber and sparky to do so and sue them for the cost. And you will win.

Was there any reason you used Dyno for this? I cannot comment too much on their competence levels, but I do understand they are bludy expensive. By FAR the best option is to have a list of trusted local traders. If you like your sparky and believe he is competent (you'll soon find out...) then ask him to recommend a local plumber he often works with too; he is bound to know people he trusts and prefers to work alongside.

grumbler

Jeepers_Creepers said:

(I understand that touching Neutrals to Earth can also cause RCDs to trip on certain systems?).

It certainly does - in systems with some noticeable current, i.e. in most systems.

Mickey666

I second the above, especially the differences between MCBs and RCDs and the suggestion that it’s a current ‘leakage’ that’s causing the problem.
This is a common failure mode in heating elements, which typically consist of a bare heating element embedded in a clay-like insulator inside a metal tube connected to earth.  If the heater becomes damaged in any way, moisture can get into the clay-like insulation and conduct a small current to the earthed casing.  This sort of failure will not trip an MCB (which requires a high current) but will trip an RCD (usually at around 30mA).  

While this is a common failure mode, it obviously shouldn’t happen with a new heating element unless, perhaps, it has been damaged in some way, either before or during installation.  

Strange that both elements exhibit the same behaviour though, which would naturally point to another problem, so having an electrician check all the wiring was definitely the right thing to do but now the results point back to the heating elements the next step is to replace them and see if that fixes the problem.  If it does then Dyno should foot the bill - including the cost of the electrician verifying there is no wiring problem, though I guess that would be an uphill struggle.

Mutton_Geoff

Mickey666 said:

I second the above, especially the differences between MCBs and RCDs and the suggestion that it’s a current ‘leakage’ that’s causing the problem.
This is a common failure mode in heating elements, which typically consist of a bare heating element embedded in a clay-like insulator inside a metal tube connected to earth.  If the heater becomes damaged in any way, moisture can get into the clay-like insulation and conduct a small current to the earthed casing.  This sort of failure will not trip an MCB (which requires a high current) but will trip an RCD (usually at around 30mA).  

While this is a common failure mode, it obviously shouldn’t happen with a new heating element unless, perhaps, it has been damaged in some way, either before or during installation.  

Strange that both elements exhibit the same behaviour though, which would naturally point to another problem, so having an electrician check all the wiring was definitely the right thing to do but now the results point back to the heating elements the next step is to replace them and see if that fixes the problem.  If it does then Dyno should foot the bill - including the cost of the electrician verifying there is no wiring problem, though I guess that would be an uphill struggle.

I thought anything with heavy current heating elements were inherently "leaky" to earth (eg immersions and ovens) and these should not be connected to the 30ma RCB protected side of the consumer unit. Could be the new ones are just more leaky than the old ones before they failed.
30ma protection is to save life if live terminals are touched. This can't usually happen on hard wired/spur type devices so they don't need the same protection.

Myser

Mutton_Geoff said:

I thought anything with heavy current heating elements were inherently "leaky" to earth (eg immersions and ovens) and these should not be connected to the 30ma RCB protected side of the consumer unit.

This is not correct, not sure where you read that?  If it was the case, then an electric shower would fall under the same category which definitely needs to be on an RCD.