# Need help heating element keeps tripping RCD



## ronan08 (Dec 21, 2019)

So after a few days of no use the machine trips when I disconnect heating element works fine any advice?


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## NJD1977 (Dec 16, 2014)

Sounds like a short in the heating element.

Need to check continuity between the element probes and the boiler casing.

If there's continuity then the element is shot.

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## ronan08 (Dec 21, 2019)

NJD1977 said:


> Sounds like a short in the heating element.
> 
> Need to check continuity between the element probes and the boiler casing.
> 
> ...


 What kind of reading am I looking for


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## NJD1977 (Dec 16, 2014)

Just had to do it on my heating element so I'm in the process of learning but you need to test the resistance using a multimeter between the electrical connection on the element and the boiler casing. Switch the multimeter to resitance ohms, level 200ohms and check If there is continuity there (i.e. zero resistance) then it means there is a path of electric that is passing from the element into the boiler casing. This earths the electric and trips the switch.

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## DavecUK (Aug 6, 2013)

You may not see it as obviously as that on a meter but it doesn't mean there isn't earth leakage from a faulty element. Sometimes it takes a megger to see it. This is because the trip current that pushes an RCD over the edge can be very low, especially if the RCD is a whole house one on the fusebox. In this case even a 10ma leakage might be enough to push the RCD over the edge as other inductive loads are bringing everything closer to the tripping point. It would be very hard to see a 10ma leakage on a meter, especially at the low voltage of the test

If it trips an MCB, then a meter will show it.


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## NJD1977 (Dec 16, 2014)

DavecUK said:


> You may not see it as obviously as that on a meter but it doesn't mean there isn't earth leakage from a faulty element. Sometimes it takes a megger to see it. This is because the trip current that pushes an RCD over the edge can be very low, especially if the RCD is a whole house one on the fusebox. In this case even a 10ma leakage might be enough to push the RCD over the edge as other inductive loads are bringing everything closer to the tripping point. It would be very hard to see a 10ma leakage on a meter, especially at the low voltage of the test
> If it trips an MCB, then a meter will show it.


But if it works fine when the element is disconnected as he said in the OP then it's highly likely its the element rather than another earth leakage elsewhere in the system, isn't it?

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## ronan08 (Dec 21, 2019)

NJD1977 said:


> Just had to do it on my heating element so I'm in the process of learning but you need to test the resistance using a multimeter between the electrical connection on the element and the boiler casing. Switch the multimeter to resitance ohms, level 200ohms and check If there is continuity there (i.e. zero resistance) then it means there is a path of electric that is passing from the element into the boiler casing. This earths the electric and trips the switch.
> 
> Sent from my SM-G973F using Tapatalk


 Ok so I'm not sure on the multimeter Its not mine but on this setting between the boiler casing and element I'm getting 3750 and rising is this alright?


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## ronan08 (Dec 21, 2019)

DavecUK said:


> You may not see it as obviously as that on a meter but it doesn't mean there isn't earth leakage from a faulty element. Sometimes it takes a megger to see it. This is because the trip current that pushes an RCD over the edge can be very low, especially if the RCD is a whole house one on the fusebox. In this case even a 10ma leakage might be enough to push the RCD over the edge as other inductive loads are bringing everything closer to the tripping point. It would be very hard to see a 10ma leakage on a meter, especially at the low voltage of the test
> 
> If it trips an MCB, then a meter will show it.


 Okay so if I take all the load off the rcb and then test will that help ie turn everything else off?


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## NJD1977 (Dec 16, 2014)

ronan08 said:


> Ok so I'm not sure on the multimeter Its not mine but on this setting between the boiler casing and element I'm getting 3750 and rising is this alright?
> <img alt="20200518_182852.thumb.jpg.c3b3d50cf9d21db83a6fcca227f26cbf.jpg" data-fileid="39768" data-src="<fileStore.core_Attachment>/monthly_2020_05/20200518_182852.thumb.jpg.c3b3d50cf9d21db83a6fcca227f26cbf.jpg" src="https://www.coffeeforums.co.uk/applications/core/interface/js/spacer.png">


3750 and rising? The photo shows OL (open loop) meaning there's no continuity.

Which is it?

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## ronan08 (Dec 21, 2019)

Oh sorry ya that was just on the table too difficult to photo while holding prongs


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## DavecUK (Aug 6, 2013)

If your getting 3750 ohm between one terminal of a disconnected heating element and the flange or side of the boiler....yes it's shot. That equates to 60+ mA more than enough to trip an RCD.

It's also probably much less resistance when hot...and at 240V rather than the 9V of your test.


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## NJD1977 (Dec 16, 2014)

ronan08 said:


> Oh sorry ya that was just on the table too difficult to photo while holding prongs


If you're getting 3750 then there's an earth leak between the element and the boiler case (earth).

Bad element I think. Unless there's any other obvious reason why the element would be transmitting current to the boiler.

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## ronan08 (Dec 21, 2019)

Okay thanks for you advise @NJD1977 and @DavecUK new element it is.


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## ronan08 (Dec 21, 2019)

@NJD1977 @DavecUK I'm struggling to find a boiler gasket can I make one out of gasket paper or instant gasket paste


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## DavecUK (Aug 6, 2013)

ronan08 said:


> @NJD1977 @DavecUK I'm struggling to find a boiler gasket can I make one out of gasket paper or instant gasket paste


 Dunno is this a trick question, because I have no idea of the machine you have, or the heating element fitment, screw in, bolt on flange, type of gasket on the machine already etc..It's sort of like the meter photo....all done to fool us 

I feel like I'm in the twilight zone.....


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## DavecUK (Aug 6, 2013)

I usually quote this movie clip as well.


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## ronan08 (Dec 21, 2019)

😂 sorry @DavecUK it's a it's a flat paper one


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## El carajillo (Mar 16, 2013)

Ask if one comes with the new element ?


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## ronan08 (Dec 21, 2019)

They dont I'm afraid


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## DavecUK (Aug 6, 2013)

But a sheet of high temp gasket material and cut out a gasket. Or try butyl rubber, nbr etc.


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## ronan08 (Dec 21, 2019)

Okay thanks @DavecUK will give that a go


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## El carajillo (Mar 16, 2013)

If you make it out then cut the inner circle first and clean up the edge. You can then place the boiler over the gasket and run a craft knife around the outside giving a clean cut.


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## Deegee (Apr 5, 2020)

For me the easiest way would be to measure the inside diameter and outside diameter and then use a compass to draw the shape of the flange then cut it out using scissors. When you've cut it out, place the gasket over the flange (great to have another pair of hands to help here) then place a ball bearing or maybe the ball pein end of a small hammer Into the indentations of the holes, strike it gently using a small hammer or mallet, the ball will cut through the gasket using the edge of the hole in the boiler as a cutter. Being an engineer I have a 12mm ball bearing brazed to a pin punch for exactly this job. HTH, DG.


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## DavecUK (Aug 6, 2013)

I'm a very bad man, I would simply poke holes in it with a screwdriver once the boiler is together and shove the bolts in (get one in first). Then cut round the outside in line with another excellent suggestion.


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## ronan08 (Dec 21, 2019)

Thank you to everyone who helped out its now working well. 🤞


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## Amvantage (Jun 20, 2018)

I know It's a bit late for this advice but the absolute minimum acceptable resistance reading between the element and earth or anything else is 2Mohms tested at twice the working voltage for single phase systems and to be honest anything close to 2Mohms probably warrants further inspection.

In my experience testing appliances and fixed wiring a good reading is usually in the 100's of Mohms and anything in the low doubles always raises and eyebrow.

not much help to you now but it might help people stumbling across this thread in the future.


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## ronan08 (Dec 21, 2019)

Amvantage said:


> I know It's a bit late for this advice but the absolute minimum acceptable resistance reading between the element and earth or anything else is 2Mohms tested at twice the working voltage for single phase systems and to be honest anything close to 2Mohms probably warrants further inspection.
> 
> In my experience testing appliances and fixed wiring a good reading is usually in the 100's of Mohms and anything in the low doubles always raises and eyebrow.
> 
> not much help to you now but it might help people stumbling across this thread in the future.


 Ok I believe I understand that. That's a clear number to have around for again thank you


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## DavecUK (Aug 6, 2013)

ronan08 said:


> Ok I believe I understand that. That's a clear number to have around for again thank you


 To use those numbers and do the tests you will need one of these. Here is a cheapie on Amazon.

https://www.amazon.co.uk/KKmoon-Digital-Insulation-Resistance-Megohmmeter/dp/B078SLXBCP/ref=pd_sbs_107_2/258-5443373-9577041?_encoding=UTF8&pd_rd_i=B078SLXBCP&pd_rd_r=732d15ee-b0ef-4caf-9145-bd6147a54a2b&pd_rd_w=1ud4v&pd_rd_wg=8CbD6&pf_rd_p=2773aa8e-42c5-4dbe-bda8-5cdf226aa078&pf_rd_r=71WAA9VR7AZX30QDT764&psc=1&refRID=71WAA9VR7AZX30QDT764


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