Oven tripping RCD

10+ year old Neff oven, just decided to trip RCD, no previous trouble.
99% of the time it's used in fan mode (where the element used is within the fan).
Just went to use it in a different mode where top and bottom elements used, but not fan, it had been heating up for a couple of minutes then tripped the RCD in its half of the CU.
Hoped it was a one-off, so reset and tried again, tripped again, wondered if the internal light was causing it so removed bulb, still tripped.
Each time after resetting RCD have to prod the timer button to "ack" the mains failure, then the electronics are on (i.e. clock flashes) if the main selector knob is "off", it doesn't trip.
If I turn temperature knob to coldest, I can turn the selector knob to the setting where just the internal light is on, it doesn't trip (a small cooling fan also runs)
Leaving selector knob in the internal light setting (i.e. no elements or main fan) then turning up the temperature knob it trips the RCD as soon as I hear the stat click on.
To me that doesn't scream "earth leaky element" but rather "gunge has got into stat or across some wiring"
Thoughts?
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Andy Burns used his keyboard to write :

Chances are, it is the element which is in use, which is failing and causing the trip. If the particular element can be seen, carefully inspect it and you might see some obvious signs of damage.
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Harry Bloomfield wrote:

Except it happens when no elements are in use, when the fan element is use, and when the top/bottom elements are in use, which is what leads me to think it's not element related.

Now it's cold again, I'll degunge it and see what happens
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Andy Burns expressed precisely :

Ah, OK. Remember a neutral leakage to earth can also trip an RCD.
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On Sunday, 17 December 2017 14:37:25 UTC, Andy Burns wrote:

Probably the clicking thing feeds one end of the element and the control switch the other. It's still most likely a bad element.
There isn't any more anyone can tell you, it's time for you to either test the elements or power it up without RCD to dry them out. Proper earthing is essential for the latter of course.
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snipped-for-privacy@gmail.com wrote:

Yeah, I was thinking the thermostat would be single-pole, but I think it's reasonable to assume from the behaviour it's double-pole with the switched neutral being common to all elements.
After it cooled down completely, I tried it once again and it did switch on for several seconds before tripping, so all it needs now is to check which of the three elements it is that's fucked, unfortunately I think that requires removing the whole oven, rather than slipping the elements out from inside the cavity, at least all spares are available.
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On 17/12/2017 14:08, Andy Burns wrote:

Screams to me knackered element.
The stat has to be switching something.
--
Adam

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ARW wrote:

I suppose an oven tripping normally would scream "element" to me, especially using one that hasn't been used for some time.
But what tempts me to think otherwise is that with the control knob in the "light" position it still trips; so it trips regardless of whether no element, fan element, top element, bottom element, top and bottom elements are selected ...

Do they tend to have an actual stat, or a thermocouple that operates a relay? You can certainly hear something click at the set point.
Double pole switching? then I suppose a fault from the neutral "end" of end element to earth would do it, even for an element that wasn't in use.
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On 17/12/2017 14:48, Andy Burns wrote:

Sure that you are not turning on the grill:-)?
The oven will use a thermocouple IMHO
Ovens are complicated things and best left for women to use.
Although they are usually piss easy to fix.
Depending on your make and model it's often only about 10 minutes work to gain access to the elements terminals and do a LE resistance test or disconnect the elements one by one and see what happens.
--
Adam

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ARW wrote:

That's why I mostly leave the oven on "fan", same as I mostly leave the washing machine on "synthetics" :-P

From youtube videos, it seems the oven probably needs to come out of the housing to access the top and bottom elements.
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On 17/12/2017 15:21, Andy Burns wrote:

Check the fan.
In a previous fan oven, we had a problem with 'gunge' collecting on the fan. I'm not suggesting your oven is dirty- the fan is tucked away and not normally cleanable as part of the normal regime.
A quick clean, and all was well.
Our current oven is 'self cleaning' but I still half expect that, it time, the fan may need a clean.
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On 17/12/2017 14:48, Andy Burns wrote:

If the element has a neutral to earth short, it can trip the RCD regardless of whether its being used or not.

It will have an actual stat of some form...

Indeed.
Can you isolate the cooker and do a neutral to earth resistance check?
--
Cheers,

John.
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John Rumm wrote:

Yes, combined DP cooker switch/socket nearby ...
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Andy Burns wrote:

We occasionally had problems at work getting mineral insulated metalclad heating elements through insulation test. Running them for a while could improve matters, but sometimes it got worse. I have a vague idea that <dot>H2O became free H2O, but the details are obscured by the mists of time.
Chris
--
Chris J Dixon Nottingham UK
snipped-for-privacy@cdixon.me.uk
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Could be as simple as knackered wiring on the stat. Many moons ago we had a Belling which had some kind of cracked insulation on a wire.
Nothing lasts forever I guess. Brian
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ARW wrote:

Dragged it out today, disconnected all elements, it would run cold without tripping, high resistance from elements to earth while still cold, reconnected elements and after warming up on fan setting for a couple of minutes it tripped, disconnected elements one by one and found the bottom element is the culprit (the most expensive and for me the least used).
While warm, the earth resistance from the dodgy element was 60k, after leaving running for 20 minutes to get decently hot, it got up to about 200k, for now its wires are taped-up and left disconnected.
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Andy Burns wrote:

Flipped the oven over and got the element out, it looks as clean as a whistle ... there seem to be only three in stock in the UK (several of the espares/4neff/partmaster websites are the same thing in disguise) all want about £50 for it.
There's one available from Holland for £13, but as mine is stamped 240V, I guess that one might actually be for 220V, so much for harmonised 230V?
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On 28/12/2017 17:01, Andy Burns wrote:

Might...
Given the small 20% possible difference in power, I'd still go for it.
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Fredxx wrote:

Seems the Dutch website is scraping items from German eBay, and it's secondhand, so I'll pass ...
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Any resistance you can measure with a multimeter is definitely defective. I would expect it to be gigaohms even at 500V.
--

Roger Hayter

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