The purpose of this guide is to provide details for trouble shooting underfloor heating system that do not appear to be heating. The document is split into three parts with the first section detailing actions that any user can carry out, and with the second and third section describing tests that should only be carried out by a qualified electrician or electrically competent person. Heat Mat’s strong recommendation is to always use a qualified electrician to carry out any tests that require the removal of a controller from the wall or the testing of an electrical circuit.

There are many reasons why an electric underfloor heating system may not be heating, and we have tried to cover most of these in this document. The tests are focussed on a heating system that is not heating at all, and although this document is written with Heat Mat underfloor heating systems in mind most of the advice can be applied to other brands of electric underfloor heating. The information below assumes that no heat is currently being felt from the electric underfloor heating system; if your system is heating but not to the desired level then it is likely that the target temperature is not set high enough, or the floor temperature limit is set too low.

Hopefully, the actions below will help you to get your system up and running again or will lead you to the further tests that are required.


Initial checks – these can be carried out by any user

These checks are designed to solve any simple issues with the controller not receiving power, or the controller not trying to switch on the heating system.

  • Fused spur – ensure that the fused spur supplying power to the controller is switched on. If it is not the controller will not power up. Very often there will be a fused spur with an on/off switch located at the base of the wall beneath the controller
  • RCD/RCBO/’Fuse’ – in the consumer unit (fuse board) there will normally be a dedicated supply for the underfloor heating, and it would usually be annotated as such. If the RCD/RCBO/’fuse’ has tripped this will stop power being sent to the heating system. Resetting the switch to allow power to reach the controller may sort out the issue. If the switch trips again then it is important to contact an electrician to examine why it is tripping
  • Controller on/off – check that the controller is turned on. With the NGTouch this is an on off switch on the left-hand side of the controller
  • Error messages – if the controller shows an error message, please contact Heat Mat with the controllers model number and the error message for guidance on how to proceed. Details of the error codes are included in the controllers instructions
  • Put the controller into boost or manual mode – put the controller into one of these modes and set the target temperature to 35°C so that the floor should start heating
  • Floor heating indication – most controllers have a graphical indicator to show that they are heating. This could be three wavy lines, a flame symbol or the temperature on the display turning red when heating. Check your controller’s instructions to confirm which indication it uses. If the indication on the screen is on for two hours but you can not feel heat coming through the floor then you should move on to the next set of tests to be carried out by an electrician. You can place a thermal block such as a towel or cushion on the floor to trap heat beneath it if the room is cold to confirm if the floor is heating or not. If the heating indicator is not coming on you should try the following
  • Maximum floor temperature – is the maximum floor temperature set high enough? Set the floor limit of the controller to 35°C to see if the controller will then send power to the underfloor heating
  • Check the floor temperature – check that the floor temperature the controller is reading is correct. On the NGTouch you can check this on the info screen, and if the floor is not warm you would expect the floor temperature to be 20°C or less. If the floor temperature is shown as much higher than this it could indicate a damaged floor sensor, the incorrect floor sensor for the controller or that the floor temperature sensor is next to a hot water pipe or similar. It may also indicate that an offset has been made to the floor sensor and to cancel this you can reset your controller
  • Check for thermal blocks – if the floor temperature sensor is beneath a thermal block that traps the heat this can lead to the controller cutting out the heating before the room is warm. Remove any thermal blocks such as rugs or dog beds from the area where the floor sensor may be located and see if this allows the system to warm up
  • System power – the NGTouch controller will provide a read out of the total system power on its info screen. The controller is rated to power 3,680W of underfloor heating at 230V and 3,840W at 240V, so if the total system power is above this level, it may cause the controller to overheat and stop powering the underfloor heating. Other controllers will have their own maximum loading and please refer to the controller’s instructions to confirm the maximum loading they are designed for
  • System Reset – as a last resort, please try and re-set the system, using the “factory reset” function which in the NGTouch is within the advanced or engineer settings
  • If none of the above checks solve the issue and the controller appears to be sending power to the heating system the next step is to test the controller as detailed below


Basic controller testing – to be carried out by an electrician

These checks are designed to locate any issues with the controller itself that have not been found with the first set of tests.

  • Check controller wiring – confirm that the controller is correctly wired in accordance with the installation instructions
  • Check for 230V input – confirm that the controller is receiving 230V input
  • Check for 230V output – reset the controller and set to tiled floor mode regardless of actual floor covering. Place the controller into manual mode or boost mode and increase the temperature until the relevant sign on the stat to show heating is apparent. Test for 230V output from the stat and if this is not present it indicates that the controller needs replacing
  • Floor temperature sensor check – carry out a resistance test on the floor sensor and confirm that the reading matches the expected resistance. On most of Heat Mat’s controllers this is 12kOhm at 25°C, but other brands of sensor may be 10kOhm, 50kOhm or 100kOhm. If an incorrect sensor has been used with the controller in many cases, you can adjust the resistance setting in the controller to allow it to read the correct floor temperature
  • If none of these checks show an issue, the next step is to test the heating mats/cables themselves


Electrical circuit testing – to be carried out by an electrician

These tests are designed to check the actual heating elements themselves and should only be carried out after all the above tests have been carried out including confirming that there is a 230V output from the controller

  • Contacted supply – if a contactor is powering the heating system this should be checked to confirm that it is switching correctly and supplying 230V to the heating mats/cables when the controller is sending out power
  • Resistance tests – the resistance reading should be taken for each of the heating mats or cables individually and this should be compared to the expected reading for each unit. These reading should be recorded and then should be provided to Heat Mat if the trouble shooting does not get the system up and running. The combined readings from the heaters can be used to confirm the total loading of the system, and this Ampage should be compared to the maximum rating on the controller to confirm that it does not exceed the safe operating limits
  • Insulation resistance test – an insulation resistance test should be run on each of the heating mats/cables individually to confirm that they are not going to earth and have not been damaged in this way. A 500V test is desirable if possible
  • If the above tests show that the resistance reading of the heaters is not as expected, or the heaters are going to earth, please contact Heat Mat’s technical support team for advice on 01444 247020
  • If the above tests do not throw up any anomalies, and there is no clear reason why the system is not heating, there is one further set of tests that can be carried out
  • Direct power to the heaters – power each of the heaters directly with a supply that includes 30mA protection. The heaters should warm up and the heat should be obvious through the floor after a maximum of two hours – use a thermal block on the floor to build up heat beneath it in very cold situation

Please record the results from all tests made as this could be very useful in troubleshooting the issues with Heat Mat’s tech team.

If you have any questions or require any further guidance please contact our award winning technical department, by phone on 01444 247020 or contact us here by email. If you prefer, we also have an online chat available between the hours of 8.30AM — 5.30PM, please click here to chat.