Frequently Asked Questions

Heating Systems

1. What floor finish is suitable for use with the devimat system?
   Most floor finishes are suitable for use with underfloor heating providing the floor has been prepared correctly and any manufacturer's temperature guidelines have been adhered to. With finishes such as wood laminates and carpets it is essential that the heating mat is completely covered with a latex levelling compound before specified finish fitted.
2. The devimat is too big for the room, can I cut it?
   The mat cannot be shortened as this will alter the resistance of the mat and it may overheat. it is important that the area to be heated is measured accurately (free floor area only) and that you always round down.
3. My fuse keeps blowing when I use the mat?
   Fuses blow or circuit breakers trip on either short circuit or on overload, short circuit being the most common cause. This will mainly be due to mechanical damage, for example the heating cable being cut, squashed or possibly drilled through.
4. Do we require insulation with devimat products?
   The devimat is designed as a retrofit product to be laid directly onto an existing floor surface, so does not require insulation. However, if there is room within the floor to add insulation or a tile-backer board this will enhance performance.
5. Does the floor need to be primed before laying the devimat?
   The mat has an adhesive backing, but if the floor is dusty or greasy it will not stick particularly well. Priming the floor will help the mat to fully adhere to the floor surface.
6. The system is not heating up!
   There are a number of reasons why this could happen.
   1. Check that you have a supply (voltage) to the thermostat.
   2. Check the thermostat is operating.
   3. Check the settings on the thermostat particularly the 'nt' setting
   4. Check the continuity and resistance of the mat.
   
   These checks may have to be carried out by a qualified electrician.
7. I have a large area that requires two mats, how do I connect them together?
   The cold tails have to be brought out of the floor and have to be connected in parallel. ie. Core colours connected together, brown with brown, blue with blue etc.
8. Which type of mat do I need to order 100W/m² or 150W/m²?
   The 100w/m² mats are for installation on wooden floors. (If wooden floor is ventilated it is important to fit some form of insulation beneath) 150w/m² mats are for installation onto concrete based floors.
9. I want to use devimat underneath a laminate flooring, what type of underlay do you recommend?
   The underlay usually supplied with wood laminate is an acoustic about 2-3mm thick, this is acceptable. If you are installing anything other than this, please call our technical team at DEVI for advice.
10. Can I put the devimat underneath a bath / shower tray / kitchen units etc.?
    DEVI does not recommend that the devimat is installed under any such fixtures for a number of reasons. 1. It can inhibit the heat being produced from the system. 2. If ever a fault was to occur it would be extremely difficult to carry out a repair.
11. I have a floor which is made up of both timber and concrete, which mat should I use?
    DEVI would recommend that each section of floor has its own 'mat' and thermostat. If one size mat and thermostat were to be used then where do you install the sensor? In this scenario the floors would deliver uneven temperatures.
12. What type of tile adhesive / levelling compound / tiling grout do you recommend?
    The covering has to be flexible or have a flexible additive.
13. How thick does the layer of tile adhesive/levelling compound need to be?
    The adhesive bed has to be thick enough to cover the cables, generally 4-5mm is sufficient.
14. How long do I have to leave the heating system, after tiling, before I can switch on?
    DEVI would recommend that the adhesive used is allowed to dry/cure naturally and to follow manufacturers recommendations.
15. How long does the heating system take to warm up?
    This depends on various factors, such as what system has been installed?
    What type of screed has been laid?
    What depth is the floor screed?
    
    This could be anything from 30 minutes for a devimat under tiles to 5-7 hours for a storage system.
16. What is the width of the mat?
    The actual width of the mat is 430mm but it is recommended that it be laid at 500mm intervals to ensure the correct gap between runs is achieved.
17. What is the difference between twin & single conductor mats?
    The difference between the two mats is the 'cold tail'. With the twin conductor mat, there is no second connection tail to return to the thermostat.
    
    With the single conductor mat there is a single cold tail at each end of the mat and they have to be brought back together at the connection point.
18. What is the black thing at the far end of the mat?
    This is the connection at the end of the twin conductor mat where the heating element is connected to the neutral return. This is manufactured within the cable.

1. How do I wire my mist free mirror mat?
   It is recommended that the mirror mats are wired into the lighting circuit, which is switched on and off with the room light. The connection to the lighting circuit can be via a box set in the wall adjacent to the mirror and sealed with a blank plate or by a joint box within an adjacent void.
2. What sizes are the mirror mats?
   There are 3 sizes:
   1 – 80mm x 60mm
   2 – 50mm x 70mm
   3 – 60mm x 60mm
   

1. How long do I have to leave the heating system, after screeding, before I can switch on?
   It is recommended that any screed be allowed to cure naturally and this would again depend upon its thickness. Generally the length of time from the screed being laid and the system being switched is sufficient for it to dry out.

Thermostats

1. How do I remove the front from the devireg 550 thermostat?
   There is a small retaining clip in the centre slot along the top of the square cover. This should be pressed with a small screwdriver; at the same time ease the cover off. As you open the thermostat box there is a piece of paper with a diagram placed on top of the thermostat showing you how to do this.
2. Why does my devireg 550 thermostat only show a 1-10 scale with devimat & bathroom applications?
   Electrical wiring regulations do not allow thermostats to be fitted within bathrooms. So, as it is placed outside the room it cannot sense the air temperature in the bathroom. Therefore the thermostat is linked to floor sensor and reads out as a comfort setting between 1-10. This is not air temperature. Each number shown on the face relates to 5°c i.e. No. 6 would relate to 30°c floor temperature.
3. Why is my devireg 540/550 thermostat coming on in timer mode, when it is not programmed to?
   There could be two reasons for this.
   
   The times programmed into the thermostat are the times you wish the room to be at the temperature set. The time it takes time to achieve this temperature is added to the start time to ensure the temperature is achieved for the start time set. ie if it takes 2 hours to achieve temperature and the time set is 7am it will switch itself on at 5am.
   
   Another reason could be that the set back or 'LO' setting has been incorrectly set during configuring the thermostat. This is the setting that directs the system to switch back on to offer frost protection. This should be set at -25°. This means that if the temperature drops 25 degrees below the temperature shown on the face it will switch back on. So, if this was incorrectly set to read -5° and the face temperature showing 21°, as soon as the temperature dropped to16° the system would switch back on.
   
   This becomes more of an issue when the thermostat is set to operate on floor sensor as the readout is a comfort setting between 1-10 , with each number relating to 5°.
   
   If the user were to turn the thermostat to 10 to 'try' and get more heat they would effectively be asking for 50° and even if the Lo setting was set at -25° the system would switch back in when the floor temperature dropped to 25° which would not take long particularly in the winter months.
4. Where can I put the thermostat?
   The thermostat should generally be positioned in the room it is controlling so it can accurately read the air temperature. It should also if possible be out of direct sunlight and away from any draughts or any alien heat source may affect it, ie a radiator or TV.
   
   Thermostats for bathrooms & en-suites have to be placed remotely either outside the door or in a cupboard and linked to a floor sensor.
5. The thermostat display is blank, what is wrong?
   This generally means there is no supply - Check
6. What does the 3 wavy line symbol mean?
   This is indicating that the temperature is ’below set point’ or has not reached the temperature set.
7. Can the thermostat be positioned inside the bathroom?
   According to electrical wiring regulations thermostats should not be fitted in rooms with a fixed bath or shower.
8. The outer ring on my devireg 540 / 550 thermostats is flashing, why?
   This is indicating there is a fault somewhere on the control system. The flashing brings your attention to the fact there is a fault at the same time it shows an error code number between 2 & 7. Refer to the booklet for what fault the code relates to.
9. My mat is the same temperature at 6.0 and when it is at 10.0?
   The reason for this is that when you set up the thermostat the 'nt' setting is the maximum temperature the floor will reach as this is the 'upper limit'. So even though you turn it up to 10 it will still switch off at whatever the 'nt' is. Incidentally each number relates to 5 degrees therefore 6 would equal 30°c.
10. What are the network terminals used for?
    These thermostats can be networked which means that a number can be linked together through the wiring with one being the master and the rest being slaves. This allows information to be programmed into the master which is then passed to the slaves.
11. What is the 'lo' setting for? Needs better explanation of what this does.
    The 'LO' setting is the 'set back' temperature. This is the temperature below that which you see on the face that the thermostat will switch back on again even in an off period, i.e. if the 'LO' setting is say -10 and the temperature showing on the face is 21, if the temperature drops to 11 degrees it will switch back on.
12. How do I mount the devireg 550 thermostat?
    The 550 is a flush mounted thermostat so requires a 47mm deep box set in the wall.
13. What is the 550 setup code?
    The code is 0044 and has to be set before any setting changes can be made. This is done by pressing and holding the grey button in for approx 12 seconds until the word ‘CODE’ appears then rotate to 0044 and press then continuing with the configurations.

1. What is the difference between the devireg 130 series and 520 series?
   The 130 series are surfaced mounted manual thermostats.
   The 520 series are a flush mounted programmable thermostats.
2. What do the lights indicate on the devireg 130 / 710 / 750 / 754 controllers?
   On the 130 series the green light indicated that the thermostat is 'on' but not charging the system. This changes to red when actually charging the system.
   
   The 710 is an anticipatory controller and has two lights, the one on the left by the 'limit' button is green when not heating and turns to red when charging. The one in the top right corner is red and will flash indicating that the floor has taken a charge on the 'off peak'.
   
   The 750 is another anticipatory controller that has two lights, one by the E6 button that shows green when not heating and changes to red when charging.
   
   The 754 is the multi-zone slave unit with a light for each zone situated to the left of the E6 control, this will be green when not heating and red when charging. The red light by the moon symbol indicates that an overnight charge has been taken and will remain on for 11 hours after the start of the charge period.

Misc

1. Do you have to use an RCD?
   The use of an RCD is recommended particularly in ‘wet’ areas such as bathrooms & en-suites. An RCD offers greater protection in the event of a fault.
2. My mat / cable has been damaged / broken, can I fix it?
   Yes all mats & cables can be repaired. DEVI offer a fault finding service
3. What is the estimated running cost of the system (mat / Cable)?
   The running cost of a cable or mat is dependant upon its rating/output and is based on the units of electricity consumed.
   
   A unit of electricity is 1000watts (1KW) for 1hour at the unit cost of electricity
   ie 1500w x Ihr x 6.5p/unit = 9.75p/hr.
   operated on ‘off peak’ this would be 1500w x 1hr x 3p/unit =4.5p/hr
   
   The devimat warm floor system costs approximately 0.5p per hour, per m2 to run.
4. How long is the warranty on DEVI products?
   All devimats/deviflex cables - 10 years.
   Thermostats – 2 years.
5. What does the DEVI warranty cover?
   All mats, cables and controls are covered against manufacturing defect.
   Any failure caused my mechanical damage will be attended to but the cost covered by the customer.
6. Can we get a DEVI technician to come out and look at the system?
   DEVI will send an engineer to attend a fault but the cost of the visit will have to be guaranteed. Any costs involved will be determined once the fault is located.
7. Which cable is live / neutral from the heating elements?
   This will vary from product to product. For twin conductor cables/mats there will be a 3 core cable attached with identifiable core colours. For single conductor mats there will be a blue & black cold tail blue being neutral and black being live. For single conductor cables both cold tails are black and there is no polarity, ie it doesn’t matter which cable is connected to live and which to the neutral.
8. Can I extend the cold tails / sensor cable?
   Both the cold tails and the sensor cables can be extended by up to 50 meters.
9. What is the maximum floor finish thickness I can have with Devimat / Deviflex heating cables?
   This will depend upon the finish specified. For timber, 20mm for soft wood, 30mm for hard wood, most wood laminates are OK but may need to be treated on merit. Most vinyls are suitable as long as manufacturers temperature limits are adhered to. Most carpets and underlays are suitable but the lower the tog rating the better as the system response times.
10. What type of supply do I need?
    This will depend upon the area being heated and the density of cable / mat installed. Your electrician should be able to calculate this once he knows the rating of the underfloor heating installed.
11. Is my underfloor heating suitable for use underneath carpets?
    Yes providing the mat / cables are covered with a latex levelling compound first.
12. Are there restrictions on what furniture I can have on top of my underfloor heating system?
    Underfloor heating relies on the heat it produces being unrestricted, if it is restricted it may cause that particular area to overheat and at worst discolour the floor. Things such as beanbags, mattresses laid directly on the floor may cause problems. Anything that allows air movement under it is OK.
13. What is a 'floor sensor'?
    A floor sensor is a limiting device that governs the upper limit temperature that the floor has been set to on the thermostat.
14. What box is the floor sensor in?
    The floor sensor is supplied in the base of the thermostat box.
15. Where is the floor sensor wired to?
    The floor sensor is wired back to the appropriate thermostat and connected into the NTC terminal. There is no polarity on the cables therefore it does not matter which cable goes in which terminal.
16. Is the floor sensor necessary? (I haven’t installed one!!!)
    The 540 /550 thermostat can be programmed to operate as air sensing, floor sensing or air & floor sensing.
    
    A floor sensor must be installed when floor, room and floor sensing is chosen.
    
    This is particularly necessary when controlling heating in bathrooms and en-suites where thermostats are placed outside the door.