Electric underfloor heating is tripping

[Why-me]

Hi all,

I've been lurker of these forums as there is a wide range of helpful information.

I'm coming to the end of a stressful kitchen extension having had issues with the builders. We've got electric underfloor heating installed on the ground floor of or house which has worked fine for the last couple of years. We decided to install the same warmup foil mat in our kitchen.

Now, I decided to test the heating. The thermostat turns on fine, allowed me to set the time etc then when the relay kicked in to warm it, it tripped the electrics. This got me really worried.

I've checked with my multimeter and the ohms reading between L N is within tolerance, however its detected earth leakage from both L N to ground. The multimeter was set at 2m ohms and when I test leakage the figure jumps and then stays at 1.

I remember the builder caused a huge leak in our kitchen when installing the water softener a month ago. We upgraded our mains to 32mm so you could imagine how much water gushed out. He tried to clear as much as possible. Last week there was a leak from the boiler area where the copper pipe was under tension going in to a push fit. That was fixed but again water was on the floor, especially around the edges. The water has most likely seeped under the floor.

My gut feeling is that I have to pull up the floor (waterproof laminate) but how can I do this when all the units and worktops have been installed? Do I have any other option? It's very depressing having waited so long after continuous issues. Should I call a specialist? I'm not sure what they would be able to do tbh in this scenario.

Any help or advice is much appreciated.

 

[Taylortwocities]

Most multimeters are not great at detecting earth leakage. A proper insulation resistance tester will check the circuit under voltage conditions (usually 500volts). A proper IR tester will give a worse result than your multimeter has!
Even your basic readings show that you have a serious issue. The mat itself should be water resistant but any joints or junctions will need drying out. Probably the area under the floor is still wet. Without ventilation this could take a very long time indeed.

If have any joints or junctions then check there first. I don’t have any other advice. Sorry.

 

[Nozzle]

Is there any chance they've screwed or nailed something through the floor?
Your meter reading "1" probably means infinite rather than 1ohm or 1Mohm. As Taylortwocities says, you can't do a proper IR test with a multimeter, as it needs a decent voltage to pass an accurately measurable current through "insulation"

Nozzle

 

[Why-me]

Is there any chance they've screwed or nailed something through the floor?
Your meter reading "1" probably means infinite rather than 1ohm or 1Mohm. As Taylortwocities says, you can't do a proper IR test with a multimeter, as it needs a decent voltage to pass an accurately measurable current through "insulation"

Nozzle

It's possible but highly unlikely they screwed something. If it was it would be near the door lining which joins the other floor but was right near the edge. Wouldn't this show up in the resistance test?

So do you think it's worth getting a heating floor specialist in before I attempt to pull up flooring and cabinets? Or should I try and dry the area somehow.

This is the dilemma I have

 

[bernardgreen]

As Taylortwocities said you need to have the UHF tested for Earth leakage using the correct test equipment before you start lifting floors.

What is tripping, is it an MCB ( no test button ) or an RCB which does have a test button ?

 

[Why-me]

It's rcd with test button. Ok, I'll be getting an electrician to come in as they have to provide the electrical certificate. The original electrician left the country. Only added to the long list of problems...

 

[bernardgreen]

It's rcd with test button. Ok, I'll be getting an electrician to come in

The UFH may not be at fault. It might be a Neutral to Earth fault elsewhere that causes the RCD when a significant load ( such as UFH ) is switched on and some of the Neutral current from that load is diverted away from the RCD by the fault.
Some electricians are unaware that this can happen and only test the circuit which appears to be causing the trip.

 

[flameport]

pull up the floor (waterproof laminate) but how can I do this when all the units and worktops have been installed?

Remove the plinths, laminate may end just behind them.
If not, cut through the laminate just behind the plinth line with a multicutter, then it can be removed without moving the cabinets or anything else.

 

[ericmark]

I had a problem when the pipes in bathroom leaked, I was abroad, so wife simply did not use the ceiling light, when I returned all I did was change bulb which had cracked and drawn in water, it had all dried out, but until dry turning on power can cause a track, and once a carbon track is formed, only option is to remove it.

I lost my insulation tester and with an internet hunt found one like this

at £35, this one says £53 but hunt for Insulation tester VC60B and you will find some for around £35, they are not calibrated so can't use them to complete official documents, but will test OK, compared mine with my mega and same readings.

I have tried using a 9 volt multi-meter, and simply no good needs the 250, 500, or 1000 volt to find faults.

I have not used "warmup foil mat" I wanted to use Raychem as self regulating, but at the time I fitted it, it was not done with an earthed braid and I was doing it in a wet room, so either earth mesh or earth braid required, the problem is the non chemical versions need a pocket and a sensor to monitor floor temperature, and the floor must not have anything placed on the heated section or it can over heat. My sensor failed, and got stuck in the pocket, it did not overheat unless on for 4 hours or more, and we only switched it on when going to use wet room. However unless you are very careful so easy to over heat a section.

 

[Why-me]

I've managed to get a price for a ufh specialised. They are charging 460+vat to locate and fix, but i will have to cut the flooring myself. Does anyone know exactly how they would fix an earth leak fault, after pin pointing the location? I thought they would only use a thermal camera if the resistance was at fault, but unsure how they would do it for an earth leakage.

 

[dannyboi2003]

Before you get the UFH Specialist in I have a couple of questions:

1. Has the UFH ever worked, I assume not as you said you switched it on to test?
2. Where did they take the supply for the UFH from, a nearby socket or have they run a dedicated circuit back to the consumer unit?

If they have installed a new circuit back to the CU then they could have made an error with the neutral connection there which would cause the RCD to trip, this would be your best case scenario and it's an easy fix. So if you can I would get an electrician in to check the supply to the UFH first.

 

[Why-me]

Before you get the UFH Specialist in I have a couple of questions:

1. Has the UFH ever worked, I assume not as you said you switched it on to test?
2. Where did they take the supply for the UFH from, a nearby socket or have they run a dedicated circuit back to the consumer unit?

If they have installed a new circuit back to the CU then they could have made an error with the neutral connection there which would cause the RCD to trip, this would be your best case scenario and it's an easy fix. So if you can I would get an electrician in to check the supply to the UFH first.

1. Not worked before, although it is a brand new system with a new thermostat.
2. It's a dedicated circuit back to the consumer unit via fused spur, although at the unit they connected it to the same fuse that is supplying existing ufh in a different area (dinning).

 

[ericmark]

I don't know how an UFH mat could be repaired, I know with mothers when the builder damaged it when laying we had to fit a complete new mat.

One thing you could do is temporary replace the fused spur for a socket and trying to plug in a kettle or some thing and seeing if that caused it to trip, that would test if error made when connecting neutral in the consumer unit.

 

[dannyboi2003]

That's a great suggestion by ericmark, if you feel competent enough change the fused spur for a socket and plug something high powered like a kettle into it and see if the RCD trips. If it does the issue is the feed to the UFH, if it doesn't then there is an issue with the UFH however this could be an issue with the controller or it's wiring and doesn't necessarily mean the heat mat is goosed.

 

[Why-me]

Thought I'd update this thread as I read lots where the op hasn't responded so don't know whether or not the issue was fixed.

In my case I gave the builder a chance to fix it and the issue was at the fused spur connection, I don't know exactly how he fixed it (he was the one to wire it) but it does work now thankfully. I'm confused though as I'm pretty sure it was leaking to earth when testing the wire mats with my multimeter, but then again that isn't the proper test?

Thank you all for the replies. I was really worried that I'd have to pull up the floor.