Tips for tracing domestic wiring issue.

[Alex Gibson]

Hi all,

I'm keen to gather any useful tips people might have before getting hands on to solve a wiring problem:

Our 'new' house has electric underfloor heating which does not work.  There were two relevant cavities in the wall, one containing the controller and another near floor level containing a chunky relay.

I've checked out the controller and it appears to work perfectly wired up on a bench.

The relay has distinctly corroded connectors, so will replace it for sure.  It could be the root cause of a wiring overload?

None of these wires seems to have live mains, whether or not a consumer unit breaker marked 'floor heat' is on.

In the control box patress there's one mains wire feeding from the top which i'd expect to be the supply, it measures 3.5V AC on live, 4.5V AC on neutral, whether or not the breaker is on.  I guess this must be inducted voltage.  

I assume there is a break in the wire somewhere, but don't have tools I'd trust other than a multimeter, to go searching for it.

Would anyone have any tips from experience as to how to trace the issue, with confidence and minimal to no destruction to plaster etc please?

Ang tips for good value but trustworthy tracing tools appreciated, I am returning an excessively cheap stud/live wire tracer I bought from Aldi, not sure what else I expected there...!

Thanks, Alex

[Tom Bayley]

I have a friend trying it with a CAT 5 fault finder

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[Andrew Harvey]

Your situation reminded of a video I watched a while back: https://youtu.be/GlUlSQrneCU

Worth a try, but not sure if your multimeter will cut it.

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[Richard Ibbotson]

If you think you are measuring ghost voltages then adding a3k3 resistor in parallel with the meter should eliminate them. Add a fast blow fuse in series with the resistor if you are not sure.

Is there mains voltage on the output of the breaker and is the wiring local to the fuse is good for both live and neutral. 

Do you have continuity and isolation for the actual heating elements?

Do you have any likely causes of wiring damage? rodents , amateurs?

Richard

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On 9 Dec 2023, at 16:54, Andrew Harvey <harvey...@gmail.com> wrote:



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[Alex Gibson]

Many good tips thank you all!

Watching the video linked

I am happy to spend householder level money for a suitable tracing tool if there is such a thing?  I've used £30 branded stud/wire finders and had only a certain level of confidence, the £15 Lidl one was an utter waste of space.

I think I have to open the consumer unit and check the breaker, will need daylight for that...

Good tips for eliminating the parasitic voltage and getting a quick blow fuse.

If anything i hoped the small AC voltage might be something I could use to trace the wire.  But as it's present with the breaker off, it's probably coming from another wire running close by...

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[Alex Gibson]

The element(s) are buried under tiles in our conservatory, I can't see any reason for the corrosion on the relay terminals let alone opportunity for rodent attack...

Measuring across the 2 elements which are wired in parallel, I get 12.7 ohms which seems plausible to me. And the thin wires I presume to be the thermistor measure 17.67kohms which again seems plausible.

The main issue is that we have no mains coming to either patress.

There is a a wall socket 30cm to the right of the lower relay patress which is live and OK.  But neither of the mains wires to the relay is live, and that would seem to be the only purpose for the top wire to the control unit patress, it just isn't live :(

[Richard Ibbotson]

12.7 ohms on 240 volts would be around 19 Amps and 4.5 kW, which sounds plausible. What is the rating of the breaker on the fuse board for that circuit. I would expect the supply cable to the patters to be larger than normal 13A cable too.

Is there voltage on direct on the output of the breaker? Might the breaker be faulty. If breaker OK the as you suggest most likely the cable  between distribution board and pattress. If this is an extension then possible damage in that route from new pipes, rodents, etc. 

If the breaker is good then you could just try bypassing cable from distribution panel direct to heating elements to test.

Interesting you say two mains wires. That suggests a ring but strange there are no other sockets not working.

Is the house wiring generally of good standard?

Are the relay contacts maybe burnt not corroded? Say if the relay was not switching cleanly?

I cannot think of any device worth buying to help. When you buy a new multimeter you various get one with Lo Z capability, but not worth it for fixing this.

Richard

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On 9 Dec 2023, at 19:35, Alex Gibson <al...@alexgibson.net> wrote:



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[Alex Gibson]

Hmm... Per attached photo of the control unit patress, the thicker twin and earth wires from the top are just under 2mm on my cheap Vernier minus battery, so fairly sure they're 2.5mm2.  So is one of the lower pairs heading down, the other is about 1mm diameter so 1mm2 or even 0.75mm2 - that will be the control wire for the relay.  Hence I'm fairly sure the top wire should be the supply, and good for 16A nominal, up to 20A max if in conduit in wall...  Breaker is nominal 20A.  

So, seemingly within ratings but not a lot of headroom!

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[Alex Gibson]

Thanks Richard, I looked again at the connectors, and while there certainly is surface corrosion there was also a bad crimp and a wire pulled right out of the connector which looked a little melty!

I'm going to document the wiring, remove and bench test the relay, it might actually be ok!

[Richard Ibbotson]

Yea please sketch out some sort of schematic. I am struggling to understand the relationship between the two boxes. On the box with the relay, is there no power coming to the thicker twin and earth at the top?

What are the white and black wires?

How far apart are the two boxes?

I assume the relay switches the live from the cable at the top to the live(black) of the heater elements. What drives the relay coil?

Let's get you warm and poor for Xmas!

Cheers,

Richard

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On 9 Dec 2023, at 21:21, Alex Gibson <al...@alexgibson.net> wrote:



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[Alex Gibson]

Hehe, yes, occasionally we may splurge and actually use it!!!

Attached photos of the context, the relay patress is directly below the control patress, right in the corner of the room.  And the back of the control unit, ignore the thin wires, I just wired up a mains plug to see if it works (yes).

I will do a schematic in the morning, having retrieved my label maker from the office, and hopefully open up the consumer unit and check the breaker, once my backup lighting fusion generator comes online in the morning.

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[Richard Ibbotson]

It does look like you are close to understanding this 

The core issue seems to be to get the power supply to the relay/heating elements at the relay box. The second box with the temperature sensor is then sort of second order.

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On 9 Dec 2023, at 22:42, Alex Gibson <al...@alexgibson.net> wrote:



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[Richard Ibbotson]

Excited to see how this works out. When the lights go dim over Aldermaston and Burghfield  we are all with you.

Not really!

Phhtzzzz!!

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On 10 Dec 2023, at 01:15, Richard Ibbotson <richard....@btinternet.com> wrote:



[Alex Gibson]

I'm pretty sure the control unit is fine, when plugged into a socket on the bench it powers up happily.  

Heading to my office for labelmaker and kit of crimp tool/spade connectors... 

The daylight is a bit feeble but I should be able to check the breaker.  The supply is the real issue as you say.

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[Alex Gibson]

Well, I've found the what of the problem of no power to the circuit...!

Now to try to figure out the why?

Previous owners said about the underfloor heating that it was not terribly effective... I knew that was disingenuous but this takes the biscuit!

[Alex Gibson]

Loitering behind the pretty full wiring of the consumer unit was one fairly chunky wire terminated in choc blocks wrapped in tape... I think this is likely my underfloor heating...

And an even thicker cable just chopped and left bare ended!

The previous owners had removed an EV charging outlet in a hurry just before moving out... I'm not impressed!  We effectively gifted a roof-full of solar panels fully installed and earning FIT to our buyers, would be nice if we'd been left with at least intact wiring if not a charge outlet :(

Will use my cat5 tester to check if there is continuity from the wrapped wires to the underfloor heating.  And doing a schematic of the wiring in the conservatory wall.