Incorrect installation

The most common mistakes when laying heating cables and mats

A common reason for the failure of underfloor heating to function is non-compliance with basic installation rules. Sometimes, an installation company performs such an obviously unprofessional installation that the investor contacts us with a request for an assessment before covering the floor with screed or sealant. More often, however, there are errors that are not completely obvious and so are discovered only when the heating fails. In such cases, the installation company carried out the installation quite carefully, but the mistakes they made prove that they did not have the necessary experience and unfortunately did not study the instructions.

This is one case when an investor asked for our opinion before the floor was covered. The heating cables are insufficiently attached, the clips are too far apart, and the cable is “floating” on the floor. If the screed had been poured, the cables may have come into contact with one another or even crossed, which would have led to the overheating and interruption of the cable. In the right half of the photo, there are loose cables in the immediate vicinity of the floor probe gooseneck, which would have...
And this is the result when heating cables cross. Long-term overheating (it can take a few days, even weeks or months) broke the insulation, the connection short-circuited and the circuit breaker was activated. The picture shows the remains of the heating cable which melted during the short circuit.
In this case, there was no direct violation of the installation regulations, but rather a lack of experience. We would definitely recommend making longer arcs so that the bend of the cable does not rest on the edge of the plastic skirting board. Even though the danger is small, the risk of damage to the casing from the skirting board cannot be ruled out completely - especially if the underfloor heating is supposed to be operating for another 50 years… On the other hand, the heating cable connector is...
The gooseneck with the floor probe must not be in contact with the heating cables. In this case, it is crossing them, and the reinforcement of the concrete is also pressing the gooseneck against the heating cable. The left part of the photo shows a general view of the exposed area with the defect, and the right part shows in detail how the heating cable was interrupted due to overheating. Deformation of the plastic by thermal stress (melting) can be seen at the edges of the broken gooseneck.
Heating cables must not cross expansion joints. There is a risk of either mechanical damage (cutting of the cable), or, as in this case, overheating of the cable. The cable passes through approximately 10 mm-thick insulation tape, which acts as an expansion filler. However, it is also a very good insulator, so the cable overheated and broke at the point of penetration.
An example of how heating cables should not be laid. A short time after installation, the underfloor heating in the bathroom stopped working, and after removing the tiles it was discovered that the heating cables were crossing incorrectly.
In this case, it may not be obvious what is wrong at first glance. The problem lies with the adhesive tape used to affix the cable to the base. Although the installation regulations do not prohibit fixation with adhesive tape, the tape must enclose the cable as tightly as possible. Notice the circled detail – the tape creates a roof over the cable which the concrete has no chance to penetrate. The tape is approximately 5 cm wide at this point, preventing heat dissipation from more than 2/3 of the heating...
This photo shows non-compliance with the minimum distance between heating cables. Cables must not be close together so as to prevent their long-term overheating. There must be a gap of at least 3 cm between heating cables. In this case, the tops of the heating loops on the mat are only 0.5 cm apart, and yet it would be enough to simply move one strip of the heating mat by approx. 5-6 cm, so that the tops of the loops were not directly opposite each other.