RCD problems with under floor heating

Anker · Jan 23, 2016

Hi All, I am after some help please. I have had a Heatcom 8.7m2 electric underfloor heating installed in my bathroom, for around two years. This has been placed under tiles. It is on most of the year and has been working fine without any problems. During the week the RCD tripped on this side of the CU. Installed on this side are two other circuits. Kitchen Lights and an Oven. I have managed to work out that the RCD only trips when the thermostat kicks in on the UFH.

The UFH is supplied via a FCU, with 13amp fuse. I have done a few tests with the UFH, which has produced the following readings.

The continuity between the L - N is 41.8 ohms. This is between the range from the manufacture, being 38 - 44 ohms.

The insulation test between L - N is 0.

The continuity between N-E is >2000 M ohms

The resistance between N - E is 0.034 M ohms

The continuity between L-E is >2000 M ohms

The resistance between L - E is 0.015 M ohms.

The resistance between the tails on the temperature probe is 11 ohms.

I can power the unit up, which starts the display. however once the heat symbol appears it trips the RCD not the MCB. I then tried removing the heating mat and just left the power load and temp sensor in. Without any heating on it showed that the current temp was 32 0C, which it clearly is not.

There has been no work carried out since the install and no obvious water ingress.

I have tested the RCD using my tester and the readings are within the range.

Short or having to pay a specialist heating engineer out at the cost of £800 + vat, any ideas to help sort this problem out would be greatly appreciated.

Thanks.

Andy™ · Jan 23, 2016

Continuity and resistance are pretty much the same thing, so you have done something wrong with your continuity readings if they really are >2000 M ohms

anyway, its dead. nothing you can do apart from get someone who can find & repair the fault, or replace it

apprentice87 · Jan 23, 2016

Anker said:
The continuity between N-E is >2000 M ohms

The resistance between N - E is 0.034 M ohms

Hi Anker, The figures you give do not make sense.. Take the above, how does the one test give two results.. You sure you know the difference between M and m ?? What tester you using...

john..

Essex1 · Jan 23, 2016

Doc Hudson · Jan 23, 2016

Anker said:
Hi All, I am after some help please. I have had a Heatcom 8.7m2 electric underfloor heating installed in my bathroom, for around two years. This has been placed under tiles. It is on most of the year and has been working fine without any problems. During the week the RCD tripped on this side of the CU. Installed on this side are two other circuits. Kitchen Lights and an Oven. I have managed to work out that the RCD only trips when the thermostat kicks in on the UFH.

Short or having to pay a specialist heating engineer out at the cost of £800 + vat, any ideas to help sort this problem out would be greatly appreciated.

Thanks.

You have not done sufficient tests to isolate or prove anything yet. you need to test all of the circuits supplied by this RCD to identify where the problem could lie. The neutral & earth are common at the fusebox to the oven, lights and UFH. For example if you have a N-E fault on the lighting circuit then current from either oven, UFH or lights could trip the RCD. I would get all circuits tested before you jump to any conclusions about the cause.

Doc H.