electric ufh under floor heating devimat power cable prob

14 Mar 2009
Reaction score
United Kingdom

re: devimat 150 problem (power cable)

i posted this in plumbing but then thought perhaps this is the better forum.

i have damaged the power cable (with a power drill!) breaking the outer insulation revealing fine copper wire (which is not live).

the mat is not heating up and i am 90% sure this is due to the power cable break however the ufh stops working every now and again (installed 4 months now) hence the 10% doubt.

the exposed copper looks like a braid/screen and the inner insulation does not seem to have broken. would this still be enough for the element to stop heating up?

can anyone advise the power cable spec so i can buy some (in case the section needs to be replaced).

by the way the thermostat (550) is not displaying any error codes. would this be expected in line with a break in the power cable?

i guess there is a small chance i drilled through the sensor cable however close examination of the plastic conduit doesn't show any breaks.

of course i will ensure that final connections are made by a part p registered sparks, just need a steer at this moment.

thanks for any help and advice!

Sponsored Links
Have you drilled through the heating cable itself, or the black part (the cold tail) which runs up the wall to the programmer?

For how long has it been cutting out? Since it was installed?

Has it not heated up since you drilled through it?

Did you (or anyone else) take a resistance measurement when it was installed?

I don't suppose the RCD has tripped and the programmer is running on battery power?
hi sparkyspike and thanks for taking the time to post the reply.

it is the cold tail that i have damaged.

on reflection it never really cut out, just sometimes wasn't hot enough - but this only really happened a few times in the last few months.

it was working fine yesterday (my wife tells me) and i had the drill out yesterday afternoon (and it has not worked since).

yes the resistance was fine when we installed it

i have just checked the rcd and it hasn't tripped (thanks for the suggestion).

what are my options now?

Sponsored Links
1. Do resistance measurement of the heating element
if this checks out OK
2. Do insulation measurement between earth of the element and the live end of the cold tail
if this checks out OK
download the DEVI troubleshooting guide from the DEVI website
here: http://www.devi.co.uk/downloads/TroubleShooter1.pdf
have a read and then call their customer support with your findings above. They are really helpful. There is a repair kit but you'll need to know what you need to repair first!

Hope this helps.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local